http://hdl.handle.net/10023/60 Wed, 19 Jun 2013 03:20:19 GMT 2013-06-19T03:20:19Z http://hdl.handle.net/10023/3691 Abstract: Modern software systems have increasingly higher expectations on their reliability, in particular if the systems are critical and real-time. The development of these complex software systems requires strong modelling and analysis methods including quantitative modelling and formal verification. Unified Modelling Language (UML) is a widely used and intuitive graphical modelling language to design complex systems, while formal models provide a theoretical support to verify system design models. However, UML models are not sufficient to guarantee correct system designs and formal models, on the other hand, are often restrictive and complex to use. It is believed that a combined approach comprising the advantages of both models can offer better designs for modern complex software development needs. This thesis focuses on the design and development of a rigorous framework based on Model Driven Development (MDD) that facilitates transformations of non-formal models into formal models for design verification. This thesis defines and describes the transformation from UML2 sequence diagrams to coloured Petri nets and proves syntactic and semantic correctness of the transformation. Additionally, we explore ways of adding information (time, probability, and hierarchy) to a design and how it can be added onto extensions of a target model. Correctness results are extended in this context. The approach in this thesis is novel and significant both in how to establish semantic and syntactic correctness of transformations, and how to explore semantic variability in the target model for formal analysis. Hence, the motivation of this thesis establishes: the UML behavioural models can be validated by correct transformation of them into formal models that can be formally analysed and verified. Wed, 26 Jun 2013 00:00:00 GMT http://hdl.handle.net/10023/3691 2013-06-26T00:00:00Z Meedeniya, Dulani Apeksha Modern software systems have increasingly higher expectations on their reliability, in particular if the systems are critical and real-time. The development of these complex software systems requires strong modelling and analysis methods including quantitative modelling and formal verification. Unified Modelling Language (UML) is a widely used and intuitive graphical modelling language to design complex systems, while formal models provide a theoretical support to verify system design models. However, UML models are not sufficient to guarantee correct system designs and formal models, on the other hand, are often restrictive and complex to use. It is believed that a combined approach comprising the advantages of both models can offer better designs for modern complex software development needs. This thesis focuses on the design and development of a rigorous framework based on Model Driven Development (MDD) that facilitates transformations of non-formal models into formal models for design verification. This thesis defines and describes the transformation from UML2 sequence diagrams to coloured Petri nets and proves syntactic and semantic correctness of the transformation. Additionally, we explore ways of adding information (time, probability, and hierarchy) to a design and how it can be added onto extensions of a target model. Correctness results are extended in this context. The approach in this thesis is novel and significant both in how to establish semantic and syntactic correctness of transformations, and how to explore semantic variability in the target model for formal analysis. Hence, the motivation of this thesis establishes: the UML behavioural models can be validated by correct transformation of them into formal models that can be formally analysed and verified. http://hdl.handle.net/10023/3412 Abstract: Decisions to deploy IT systems on public Infrastructure-as-a-Service clouds can be complicated as evaluating the benefits, risks and costs of using such clouds is not straightforward. The aim of this project was to investigate the challenges that enterprises face when making system deployment decisions in public clouds, and to develop vendor-neutral tools to inform decision makers during this process. Three tools were developed to support decision makers: 1. Cloud Suitability Checklist: a simple list of questions to provide a rapid assessment of the suitability of public IaaS clouds for a specific IT system. 2. Benefits and Risks Assessment tool: a spreadsheet that includes the general benefits and risks of using public clouds; this provides a starting point for risk assessment and helps organisations start discussions about cloud adoption. 3. Elastic Cost Modelling: a tool that enables decision makers to model their system deployment options in public clouds and forecast their costs. These three tools collectively enable decision makers to investigate the benefits, risks and costs of using public clouds, and effectively support them in making system deployment decisions. Data was collected from five case studies and hundreds of users to evaluate the effectiveness of the tools. This data showed that the cost effectiveness of using public clouds is situation dependent rather than universally less expensive than traditional forms of IT provisioning. Running systems on the cloud using a traditional 'always on' approach can be less cost effective than on-premise servers, and the elastic nature of the cloud has to be considered if costs are to be reduced. Decision makers have to model the variations in resource usage and their systems' deployment options to obtain accurate cost estimates. Performing upfront cost modelling is beneficial as there can be significant cost differences between different cloud providers, and different deployment options within a single cloud. During such modelling exercises, the variations in a system's load (over time) must be taken into account to produce more accurate cost estimates, and the notion of elasticity patterns that is presented in this thesis provides one simple way to do this. Wed, 26 Jun 2013 00:00:00 GMT http://hdl.handle.net/10023/3412 2013-06-26T00:00:00Z Khajeh-Hosseini, Ali Decisions to deploy IT systems on public Infrastructure-as-a-Service clouds can be complicated as evaluating the benefits, risks and costs of using such clouds is not straightforward. The aim of this project was to investigate the challenges that enterprises face when making system deployment decisions in public clouds, and to develop vendor-neutral tools to inform decision makers during this process. Three tools were developed to support decision makers: 1. Cloud Suitability Checklist: a simple list of questions to provide a rapid assessment of the suitability of public IaaS clouds for a specific IT system. 2. Benefits and Risks Assessment tool: a spreadsheet that includes the general benefits and risks of using public clouds; this provides a starting point for risk assessment and helps organisations start discussions about cloud adoption. 3. Elastic Cost Modelling: a tool that enables decision makers to model their system deployment options in public clouds and forecast their costs. These three tools collectively enable decision makers to investigate the benefits, risks and costs of using public clouds, and effectively support them in making system deployment decisions. Data was collected from five case studies and hundreds of users to evaluate the effectiveness of the tools. This data showed that the cost effectiveness of using public clouds is situation dependent rather than universally less expensive than traditional forms of IT provisioning. Running systems on the cloud using a traditional 'always on' approach can be less cost effective than on-premise servers, and the elastic nature of the cloud has to be considered if costs are to be reduced. Decision makers have to model the variations in resource usage and their systems' deployment options to obtain accurate cost estimates. Performing upfront cost modelling is beneficial as there can be significant cost differences between different cloud providers, and different deployment options within a single cloud. During such modelling exercises, the variations in a system's load (over time) must be taken into account to produce more accurate cost estimates, and the notion of elasticity patterns that is presented in this thesis provides one simple way to do this. http://hdl.handle.net/10023/3225 Abstract: Opportunistic networks provide an ad hoc communication medium without the need for an infrastructure network, by leveraging human encounters and mobile devices. Routing protocols in opportunistic networks frequently rely upon encounter histories to build up meaningful data to use for informed routing decisions. This thesis shows that it is possible to use pre-existing social-network information to improve existing opportunistic routing protocols, and that these self-reported social networks have a particular benefit when used to bootstrap an opportunistic routing protocol. Frequently, opportunistic routing protocols require users to relay messages on behalf of one another: an act that incurs a cost to the relaying node. Nodes may wish to avoid this forwarding cost by not relaying messages. Opportunistic networks need to incentivise participation and discourage the selfish behaviour. This thesis further presents an incentive mechanism that uses self-reported social networks to construct and maintain reputation and trust relationships between participants, and demonstrates its superior performance over existing incentive mechanisms. Tue, 19 Jun 2012 00:00:00 GMT http://hdl.handle.net/10023/3225 2012-06-19T00:00:00Z Bigwood, Greg Opportunistic networks provide an ad hoc communication medium without the need for an infrastructure network, by leveraging human encounters and mobile devices. Routing protocols in opportunistic networks frequently rely upon encounter histories to build up meaningful data to use for informed routing decisions. This thesis shows that it is possible to use pre-existing social-network information to improve existing opportunistic routing protocols, and that these self-reported social networks have a particular benefit when used to bootstrap an opportunistic routing protocol. Frequently, opportunistic routing protocols require users to relay messages on behalf of one another: an act that incurs a cost to the relaying node. Nodes may wish to avoid this forwarding cost by not relaying messages. Opportunistic networks need to incentivise participation and discourage the selfish behaviour. This thesis further presents an incentive mechanism that uses self-reported social networks to construct and maintain reputation and trust relationships between participants, and demonstrates its superior performance over existing incentive mechanisms. http://hdl.handle.net/10023/3205 Abstract: As computing devices become increasingly portable, it is becoming necessary to support Mobility as a core network functionality. The availability of devices such as smartphones, tablets, laptops as well as wireless network infrastructure is opening up the possibility of using Network Mobility to cater for multiple mobile nodes simultaneously. Network mobility may be useful in a number of mobile scenarios, where a large number of mobile nodes are moving in unison. A number of operational benefits stand to be gained by aggregating these nodes into a single mobile unit. Unfortunately, the current state for network mobility support, especially in terms of network layer protocols, is limited. This is in part due to the inherent complexity of mobile network scenarios, the high cost of testing mobile network protocols in operational environments and the difficulties in implementing such protocols. This thesis looks at how network mobility support may be better enabled by making experimentation with mobile networks more accessible. It shows this by first showing how analytical approaches can be useful in mobile network applications, as they abstract away from experimental details and allow for more straight forward protocol comparisons. It then goes on to look at the tools available to study mobile network protocols, where it introduces and extends an existing tool that uses virtual machines to allow for the study of mobile network protocols. Finally, it demonstrates a practical method in which mobile network support may be easily enabled in a practical setting. Fri, 30 Nov 2012 00:00:00 GMT http://hdl.handle.net/10023/3205 2012-11-30T00:00:00Z Rehunathan, Devan As computing devices become increasingly portable, it is becoming necessary to support Mobility as a core network functionality. The availability of devices such as smartphones, tablets, laptops as well as wireless network infrastructure is opening up the possibility of using Network Mobility to cater for multiple mobile nodes simultaneously. Network mobility may be useful in a number of mobile scenarios, where a large number of mobile nodes are moving in unison. A number of operational benefits stand to be gained by aggregating these nodes into a single mobile unit. Unfortunately, the current state for network mobility support, especially in terms of network layer protocols, is limited. This is in part due to the inherent complexity of mobile network scenarios, the high cost of testing mobile network protocols in operational environments and the difficulties in implementing such protocols. This thesis looks at how network mobility support may be better enabled by making experimentation with mobile networks more accessible. It shows this by first showing how analytical approaches can be useful in mobile network applications, as they abstract away from experimental details and allow for more straight forward protocol comparisons. It then goes on to look at the tools available to study mobile network protocols, where it introduces and extends an existing tool that uses virtual machines to allow for the study of mobile network protocols. Finally, it demonstrates a practical method in which mobile network support may be easily enabled in a practical setting. http://hdl.handle.net/10023/3200 Abstract: Although CSR has been the subject of substantial academic research for more than half a century, the CSR literature is dominated by empirical studies in the industrialized countries. There is limited knowledge on how CSR is perceived and implemented by companies in developing countries. This research is trying to answer those questions: what has been reported in China? Which stakeholder groups are the most important stakeholder groups in China? What is the content of CSR reports in China? And what factors are associated with CSR reporting in China, in terms of culture, political and legal system, ownership, size and industry? Based on a content analysis approach, this paper aims to identify the determinants of corporate social responsibility (CSR) reporting in China using stand-alone reports of the top 500 Chinese companies from 2006 to 2010. It is found that CSR reporting is positive associated with various factors. In addition, companies in environmental sensitive industries tend to report more environmental responsibility information than others. State-Owned Enterprises are not doing better than other types of companies. Laws, regulations or guidelines have little impacts on the reporting in China. Also the government is not one of the most important stakeholders in China. The research results support the stakeholder theory in an emerging market with important and relevant insights for enterprise managers interested in exploiting the reports as a tool to communicate with their stakeholders. Fri, 30 Nov 2012 00:00:00 GMT http://hdl.handle.net/10023/3200 2012-11-30T00:00:00Z Du, Yaning Although CSR has been the subject of substantial academic research for more than half a century, the CSR literature is dominated by empirical studies in the industrialized countries. There is limited knowledge on how CSR is perceived and implemented by companies in developing countries. This research is trying to answer those questions: what has been reported in China? Which stakeholder groups are the most important stakeholder groups in China? What is the content of CSR reports in China? And what factors are associated with CSR reporting in China, in terms of culture, political and legal system, ownership, size and industry? Based on a content analysis approach, this paper aims to identify the determinants of corporate social responsibility (CSR) reporting in China using stand-alone reports of the top 500 Chinese companies from 2006 to 2010. It is found that CSR reporting is positive associated with various factors. In addition, companies in environmental sensitive industries tend to report more environmental responsibility information than others. State-Owned Enterprises are not doing better than other types of companies. Laws, regulations or guidelines have little impacts on the reporting in China. Also the government is not one of the most important stakeholders in China. The research results support the stakeholder theory in an emerging market with important and relevant insights for enterprise managers interested in exploiting the reports as a tool to communicate with their stakeholders. http://hdl.handle.net/10023/3199 Abstract: Distributed software systems that are designed to run over workstation machines within organisations are termed workstation-based. Workstation-based systems are characterised by dynamically changing sets of machines that are used primarily for other, user-centric tasks. They must be able to adapt to and utilize spare capacity when and where it is available, and ensure that the non-availability of an individual machine does not affect the availability of the system. This thesis focuses on the requirements and design of a workstation-based database system, which is motivated by an analysis of existing database architectures that are typically run over static, specially provisioned sets of machines. A typical clustered database system — one that is run over a number of specially provisioned machines — executes queries interactively, returning a synchronous response to applications, with its data made durable and resilient to the failure of machines. There are no existing workstation-based databases. Furthermore, other workstation-based systems do not attempt to achieve the requirements of interactivity and durability, because they are typically used to execute asynchronous batch processing jobs that tolerate data loss — results can be re-computed. These systems use external servers to store the final results of computations rather than workstation machines. This thesis describes the design and implementation of a workstation-based database system and investigates its viability by evaluating its performance against existing clustered database systems and testing its availability during machine failures. Fri, 30 Nov 2012 00:00:00 GMT http://hdl.handle.net/10023/3199 2012-11-30T00:00:00Z Macdonald, Angus Distributed software systems that are designed to run over workstation machines within organisations are termed workstation-based. Workstation-based systems are characterised by dynamically changing sets of machines that are used primarily for other, user-centric tasks. They must be able to adapt to and utilize spare capacity when and where it is available, and ensure that the non-availability of an individual machine does not affect the availability of the system. This thesis focuses on the requirements and design of a workstation-based database system, which is motivated by an analysis of existing database architectures that are typically run over static, specially provisioned sets of machines. A typical clustered database system — one that is run over a number of specially provisioned machines — executes queries interactively, returning a synchronous response to applications, with its data made durable and resilient to the failure of machines. There are no existing workstation-based databases. Furthermore, other workstation-based systems do not attempt to achieve the requirements of interactivity and durability, because they are typically used to execute asynchronous batch processing jobs that tolerate data loss — results can be re-computed. These systems use external servers to store the final results of computations rather than workstation machines. This thesis describes the design and implementation of a workstation-based database system and investigates its viability by evaluating its performance against existing clustered database systems and testing its availability during machine failures. http://hdl.handle.net/10023/3193 Abstract: Mobile devices equipped with features (e.g., camera, network connectivity and media player) are increasingly being used for different tasks such as web browsing, document reading and photography. While the portability of mobile devices makes them desirable for pervasive access to information, their small screen real-estate often imposes restrictions on the amount of information that can be displayed and manipulated on them. On the other hand, large displays have become commonplace in many outdoor as well as indoor environments. While they provide an efficient way of presenting and disseminating information, they provide little support for digital interactivity or physical accessibility. Researchers argue that mobile phones provide an efficient and portable way of interacting with large displays, and the latter can overcome the limitations of the small screens of mobile devices by providing a larger presentation and interaction space. However, distributing user interface (UI) elements across a mobile device and a large display can cause switching of visual attention and that may affect task performance. This thesis specifically explores how the switching of visual attention across a handheld mobile device and a vertical large display can affect a single user's task performance during mobile interaction with large displays. It introduces a taxonomy based on the factors associated with the visual arrangement of Multi Display User Interfaces (MDUIs) that can influence visual attention switching during interaction with MDUIs. It presents an empirical analysis of the effects of different distributions of input and output across mobile and large displays on the user's task performance, subjective workload and preference in the multiple-widget selection task, and in visual search tasks with maps, texts and photos. Experimental results show that the selection of multiple widgets replicated on the mobile device as well as on the large display, versus those shown only on the large display, is faster despite the cost of initial attention switching in the former. On the other hand, a hybrid UI configuration where the visual output is distributed across the mobile and large displays is the worst, or equivalent to the worst, configuration in all the visual search tasks. A mobile device-controlled large display configuration performs best in the map search task and equal to best (i.e., tied with a mobile-only configuration) in text- and photo-search tasks. Fri, 30 Nov 2012 00:00:00 GMT http://hdl.handle.net/10023/3193 2012-11-30T00:00:00Z Rashid, Umar Mobile devices equipped with features (e.g., camera, network connectivity and media player) are increasingly being used for different tasks such as web browsing, document reading and photography. While the portability of mobile devices makes them desirable for pervasive access to information, their small screen real-estate often imposes restrictions on the amount of information that can be displayed and manipulated on them. On the other hand, large displays have become commonplace in many outdoor as well as indoor environments. While they provide an efficient way of presenting and disseminating information, they provide little support for digital interactivity or physical accessibility. Researchers argue that mobile phones provide an efficient and portable way of interacting with large displays, and the latter can overcome the limitations of the small screens of mobile devices by providing a larger presentation and interaction space. However, distributing user interface (UI) elements across a mobile device and a large display can cause switching of visual attention and that may affect task performance. This thesis specifically explores how the switching of visual attention across a handheld mobile device and a vertical large display can affect a single user's task performance during mobile interaction with large displays. It introduces a taxonomy based on the factors associated with the visual arrangement of Multi Display User Interfaces (MDUIs) that can influence visual attention switching during interaction with MDUIs. It presents an empirical analysis of the effects of different distributions of input and output across mobile and large displays on the user's task performance, subjective workload and preference in the multiple-widget selection task, and in visual search tasks with maps, texts and photos. Experimental results show that the selection of multiple widgets replicated on the mobile device as well as on the large display, versus those shown only on the large display, is faster despite the cost of initial attention switching in the former. On the other hand, a hybrid UI configuration where the visual output is distributed across the mobile and large displays is the worst, or equivalent to the worst, configuration in all the visual search tasks. A mobile device-controlled large display configuration performs best in the map search task and equal to best (i.e., tied with a mobile-only configuration) in text- and photo-search tasks. http://hdl.handle.net/10023/3176 Abstract: Society is challenging systems engineers by demanding increasingly complex and integrated IT systems (Northrop et al., 2006; RAE, 2004) e.g. integrated enterprise resource planning systems, integrated healthcare systems and business critical services provisioned using cloud based resources. These types of IT system are often systems-of-systems (SoS). That is to say they are composed of multiple systems that are operated and managed by independent parties and are distributed across multiple organisational boundaries, geographies or legal jurisdictions (Maier, 1998). SoS are notorious for becoming problematic due to interconnected technical and social issues. Practitioners claim that they are ill equipped to deal with the sociotechnical challenges posed by system-of-systems. One of these challenges is to identify the socio-technical threats associated with building, operating and managing systems whose parts are distributed across organisational boundaries. Another is how to troubleshoot these systems when they exhibit undesirable behaviour. This thesis aims to provide a modelling abstraction and an extensible technique that enables practitioners to identify socio-technical threats prior to implementation and troubleshoot SoS post-implementation. This thesis evaluates existing modelling abstractions for their suitability to represent SoS and suggests that an agent-responsibility based modelling abstraction may provide a practical and scalable way of representing SoS for socio-technical threat identification and troubleshooting. The practicality and scalability of the abstraction is explored through the use of case studies that motivate the extension of existing responsibility-based techniques so that new classes of system (coalitions-of-systems) and new classes of threat (agent-related threats) may be analysed. This thesis concludes that the notion of ‘responsibility’ is a promising abstraction for representing and analysing systems that are composed of parts that are independently managed and maintained by agents spanning multiple organisational boundaries e.g. systems-of-systems, enterprise-scale systems. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10023/3176 2012-01-01T00:00:00Z Greenwood, David Society is challenging systems engineers by demanding increasingly complex and integrated IT systems (Northrop et al., 2006; RAE, 2004) e.g. integrated enterprise resource planning systems, integrated healthcare systems and business critical services provisioned using cloud based resources. These types of IT system are often systems-of-systems (SoS). That is to say they are composed of multiple systems that are operated and managed by independent parties and are distributed across multiple organisational boundaries, geographies or legal jurisdictions (Maier, 1998). SoS are notorious for becoming problematic due to interconnected technical and social issues. Practitioners claim that they are ill equipped to deal with the sociotechnical challenges posed by system-of-systems. One of these challenges is to identify the socio-technical threats associated with building, operating and managing systems whose parts are distributed across organisational boundaries. Another is how to troubleshoot these systems when they exhibit undesirable behaviour. This thesis aims to provide a modelling abstraction and an extensible technique that enables practitioners to identify socio-technical threats prior to implementation and troubleshoot SoS post-implementation. This thesis evaluates existing modelling abstractions for their suitability to represent SoS and suggests that an agent-responsibility based modelling abstraction may provide a practical and scalable way of representing SoS for socio-technical threat identification and troubleshooting. The practicality and scalability of the abstraction is explored through the use of case studies that motivate the extension of existing responsibility-based techniques so that new classes of system (coalitions-of-systems) and new classes of threat (agent-related threats) may be analysed. This thesis concludes that the notion of ‘responsibility’ is a promising abstraction for representing and analysing systems that are composed of parts that are independently managed and maintained by agents spanning multiple organisational boundaries e.g. systems-of-systems, enterprise-scale systems. http://hdl.handle.net/10023/3170 Abstract: This research contributes to the field of ontology-based semantic matching techniques and also to the field of Instant Messaging (IM) based enhanced presence. It aims to achieve a mutually beneficial development of two fields through interactions in their use of data and their functionality. With respect to semantic matching this research has developed a collaborative and self-evolutionary approach based on user involvement in order to overcome disadvantages of traditional ontology-based approaches. At the same time, enhanced semantic matching algorithms were also explored and developed to achieve better performance when searching and querying through the ontology. In order to realize this automatic, dynamic and collaborative approach, a Jabber-based IM system was built to support its development with specific data and to evaluate its performance. In the prototype of the system, Computer Science area is selected to be the domain of the ontology in order to demonstrate the practicability of the new approach. With respect to enhanced presence an efficient semantic-based contacts search engine which can feature context-based search ranking is provided to support academic researchers. It is especially designed to help new academic researchers to find potential contacts who share a common research interest. It enriches the IM system’s presence information, and helps the user to pick the most suitable contacts and conveniently organize meetings or co-operating with others. Consequently, this research improves the efficiency of users’ academic researching, and extends users’ relationship radius during their academic research careers. The contributions are particularly highlighted by the comprehensive support during the academic user’s self-educational process. Tue, 28 Aug 2012 00:00:00 GMT http://hdl.handle.net/10023/3170 2012-08-28T00:00:00Z Zhai, Ying This research contributes to the field of ontology-based semantic matching techniques and also to the field of Instant Messaging (IM) based enhanced presence. It aims to achieve a mutually beneficial development of two fields through interactions in their use of data and their functionality. With respect to semantic matching this research has developed a collaborative and self-evolutionary approach based on user involvement in order to overcome disadvantages of traditional ontology-based approaches. At the same time, enhanced semantic matching algorithms were also explored and developed to achieve better performance when searching and querying through the ontology. In order to realize this automatic, dynamic and collaborative approach, a Jabber-based IM system was built to support its development with specific data and to evaluate its performance. In the prototype of the system, Computer Science area is selected to be the domain of the ontology in order to demonstrate the practicability of the new approach. With respect to enhanced presence an efficient semantic-based contacts search engine which can feature context-based search ranking is provided to support academic researchers. It is especially designed to help new academic researchers to find potential contacts who share a common research interest. It enriches the IM system’s presence information, and helps the user to pick the most suitable contacts and conveniently organize meetings or co-operating with others. Consequently, this research improves the efficiency of users’ academic researching, and extends users’ relationship radius during their academic research careers. The contributions are particularly highlighted by the comprehensive support during the academic user’s self-educational process. http://hdl.handle.net/10023/3090 Abstract: Multi User Virtual Environments (MUVE) are a new class of Internet application with a significant user base. This thesis adds to our understanding of how MUVE network traffic fits into the mix of Internet traffic, and how this relates to the application's needs. MUVEs differ from established Internet traffic types in their requirements from the network. They differ from traditional data traffic in that they have soft real-time constraints, from game traffic in that their bandwidth requirements are higher, and from audio and video streaming traffic in that their data streams can be decomposed into elements that require different qualities of service. This work shows how real-time adaptive measurement based congestion control can be applied to MUVE streams so that they can be made more responsive to changes in network conditions than other real-time traffic and existing MUVE clients. It is shown that a combination of adaptive congestion control and differential Quality of Service (QoS) can increase the range of conditions under which MUVEs both get sufficient bandwidth and are Transport Control Protocol (TCP) fair. The design, implementation and evaluation of an adaptive traffic management system is described. The system has been implemented in a modified client, which allows the MUVE to be made TCP fair without changing the server. Wed, 30 Nov 2011 00:00:00 GMT http://hdl.handle.net/10023/3090 2011-11-30T00:00:00Z Oliver, Iain Angus Multi User Virtual Environments (MUVE) are a new class of Internet application with a significant user base. This thesis adds to our understanding of how MUVE network traffic fits into the mix of Internet traffic, and how this relates to the application's needs. MUVEs differ from established Internet traffic types in their requirements from the network. They differ from traditional data traffic in that they have soft real-time constraints, from game traffic in that their bandwidth requirements are higher, and from audio and video streaming traffic in that their data streams can be decomposed into elements that require different qualities of service. This work shows how real-time adaptive measurement based congestion control can be applied to MUVE streams so that they can be made more responsive to changes in network conditions than other real-time traffic and existing MUVE clients. It is shown that a combination of adaptive congestion control and differential Quality of Service (QoS) can increase the range of conditions under which MUVEs both get sufficient bandwidth and are Transport Control Protocol (TCP) fair. The design, implementation and evaluation of an adaptive traffic management system is described. The system has been implemented in a modified client, which allows the MUVE to be made TCP fair without changing the server. http://hdl.handle.net/10023/2841 Abstract: The Algorithm Selection Problem is to select the most appropriate way for solving a problem given a choice of different ways. Some of the most prominent and successful applications come from Artificial Intelligence and in particular combinatorial search problems. Machine Learning has established itself as the de facto way of tackling the Algorithm Selection Problem. Yet even after a decade of intensive research, there are no established guidelines as to what kind of Machine Learning to use and how. This dissertation presents an overview of the field of Algorithm Selection and associated research and highlights the fundamental questions left open and problems facing practitioners. In a series of case studies, it underlines the difficulty of doing Algorithm Selection in practice and tackles issues related to this. The case studies apply Algorithm Selection techniques to new problem domains and show how to achieve significant performance improvements. Lazy learning in constraint solving and the implementation of the alldifferent constraint are the areas in which we improve on the performance of current state of the art systems. The case studies furthermore provide empirical evidence for the effectiveness of using the misclassification penalty as an input to Machine Learning. After having established the difficulty, we present an effective technique for reducing it. Machine Learning ensembles are a way of reducing the background knowledge and experimentation required from the researcher while increasing the robustness of the system. Ensembles do not only decrease the difficulty, but can also increase the performance of Algorithm Selection systems. They are used to much the same ends in Machine Learning itself. We finally tackle one of the great remaining challenges of Algorithm Selection -- which Machine Learning technique to use in practice. Through a large-scale empirical evaluation on diverse data taken from Algorithm Selection applications in the literature, we establish recommendations for Machine Learning algorithms that are likely to perform well in Algorithm Selection for combinatorial search problems. The recommendations are based on strong empirical evidence and additional statistical simulations. The research presented in this dissertation significantly reduces the knowledge threshold for researchers who want to perform Algorithm Selection in practice. It makes major contributions to the field of Algorithm Selection by investigating fundamental issues that have been largely ignored by the research community so far. Wed, 20 Jun 2012 00:00:00 GMT http://hdl.handle.net/10023/2841 2012-06-20T00:00:00Z Kotthoff, Lars The Algorithm Selection Problem is to select the most appropriate way for solving a problem given a choice of different ways. Some of the most prominent and successful applications come from Artificial Intelligence and in particular combinatorial search problems. Machine Learning has established itself as the de facto way of tackling the Algorithm Selection Problem. Yet even after a decade of intensive research, there are no established guidelines as to what kind of Machine Learning to use and how. This dissertation presents an overview of the field of Algorithm Selection and associated research and highlights the fundamental questions left open and problems facing practitioners. In a series of case studies, it underlines the difficulty of doing Algorithm Selection in practice and tackles issues related to this. The case studies apply Algorithm Selection techniques to new problem domains and show how to achieve significant performance improvements. Lazy learning in constraint solving and the implementation of the alldifferent constraint are the areas in which we improve on the performance of current state of the art systems. The case studies furthermore provide empirical evidence for the effectiveness of using the misclassification penalty as an input to Machine Learning. After having established the difficulty, we present an effective technique for reducing it. Machine Learning ensembles are a way of reducing the background knowledge and experimentation required from the researcher while increasing the robustness of the system. Ensembles do not only decrease the difficulty, but can also increase the performance of Algorithm Selection systems. They are used to much the same ends in Machine Learning itself. We finally tackle one of the great remaining challenges of Algorithm Selection -- which Machine Learning technique to use in practice. Through a large-scale empirical evaluation on diverse data taken from Algorithm Selection applications in the literature, we establish recommendations for Machine Learning algorithms that are likely to perform well in Algorithm Selection for combinatorial search problems. The recommendations are based on strong empirical evidence and additional statistical simulations. The research presented in this dissertation significantly reduces the knowledge threshold for researchers who want to perform Algorithm Selection in practice. It makes major contributions to the field of Algorithm Selection by investigating fundamental issues that have been largely ignored by the research community so far. http://hdl.handle.net/10023/2540 Abstract: Large-scale heterogeneous distributed computing environments (such as Computational Grids and Clouds) offer the promise of access to a vast amount of computing resources at a relatively low cost. In order to ease the application development and deployment on such complex environments, high-level parallel programming languages exist that need to be supported by sophisticated runtime systems. One of the main problems that these runtime systems need to address is dynamic load balancing that ensures that no resources in the environment are underutilised or overloaded with work. This thesis deals with the problem of obtaining good speedups for irregular applications on heterogeneous distributed computing environments. It focuses on workstealing techniques that can be used for load balancing during the execution of irregular applications. It specifically addresses two problems that arise during work-stealing: where thieves should look for work during the application execution and how victims should respond to steal attempts. In particular, we describe and implement a new Feudal Stealing algorithm and also we describe and implement new granularity-driven task selection policies in the SCALES simulator, which is a work-stealing simulator developed for this thesis. In addition, we present the comprehensive evaluation of the Feudal Stealing algorithm and the granularity-driven task selection policies using the simulations of a large class of regular and irregular parallel applications on a wide range of computing environments. We show how the Feudal Stealing algorithm and the granularity-driven task selection policies bring significant improvements in speedups of irregular applications, compared to the state-of-the-art work-stealing algorithms. Furthermore, we also present the implementation of the task selection policies in the Grid-GUM runtime system [AZ06] for Glasgow Parallel Haskell (GpH) [THLPJ98], in addition to the implementation in SCALES, and we also present the evaluation of this implementation on a large set of synthetic applications. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10023/2540 2012-01-01T00:00:00Z Janjic, Vladimir Large-scale heterogeneous distributed computing environments (such as Computational Grids and Clouds) offer the promise of access to a vast amount of computing resources at a relatively low cost. In order to ease the application development and deployment on such complex environments, high-level parallel programming languages exist that need to be supported by sophisticated runtime systems. One of the main problems that these runtime systems need to address is dynamic load balancing that ensures that no resources in the environment are underutilised or overloaded with work. This thesis deals with the problem of obtaining good speedups for irregular applications on heterogeneous distributed computing environments. It focuses on workstealing techniques that can be used for load balancing during the execution of irregular applications. It specifically addresses two problems that arise during work-stealing: where thieves should look for work during the application execution and how victims should respond to steal attempts. In particular, we describe and implement a new Feudal Stealing algorithm and also we describe and implement new granularity-driven task selection policies in the SCALES simulator, which is a work-stealing simulator developed for this thesis. In addition, we present the comprehensive evaluation of the Feudal Stealing algorithm and the granularity-driven task selection policies using the simulations of a large class of regular and irregular parallel applications on a wide range of computing environments. We show how the Feudal Stealing algorithm and the granularity-driven task selection policies bring significant improvements in speedups of irregular applications, compared to the state-of-the-art work-stealing algorithms. Furthermore, we also present the implementation of the task selection policies in the Grid-GUM runtime system [AZ06] for Glasgow Parallel Haskell (GpH) [THLPJ98], in addition to the implementation in SCALES, and we also present the evaluation of this implementation on a large set of synthetic applications. http://hdl.handle.net/10023/2533 Abstract: Random NP-Complete problems have come under study as an important tool used in the analysis of optimization algorithms and help in our understanding of how to properly address issues of computational intractability. In this thesis, the Number Partition Problem and the Hamiltonian Cycle Problem are taken as representative NP-Complete classes. Numerical evidence is presented for a phase transition in the probability of solution when a modified Lévy-Stable distribution is used in instance creation for each. Numerical evidence is presented that show hard random instances exist near the critical threshold for the Hamiltonian Cycle problem. A choice of order parameter for the Number Partition Problem’s phase transition is also given. Finding Hamiltonian Cycles in Erdös-Rényi random graphs is well known to have almost sure polynomial time algorithms, even near the critical threshold. To the author’s knowledge, the graph ensemble presented is the first candidate, without specific graph structure built in, to generate graphs whose Hamiltonicity is intrinsically hard to determine. Random graphs are chosen via their degree sequence generated from a discretized form of Lévy-Stable distributions. Graphs chosen from this distribution still show a phase transition and appear to have a pickup in search cost for the algorithms considered. Search cost is highly dependent on the particular algorithm used and the graph ensemble is presented only as a potential graph ensemble to generate intrinsically hard graphs that are difficult to test for Hamiltonicity. Number Partition Problem instances are created by choosing each element in the list from a modified Lévy-Stable distribution. The Number Partition Problem has no known good approximation algorithms and so only numerical evidence to show the phase transition is provided without considerable focus on pickup in search cost for the solvers used. The failure of current approximation algorithms and potential candidate approximation algorithms are discussed. Tue, 01 Nov 2011 00:00:00 GMT http://hdl.handle.net/10023/2533 2011-11-01T00:00:00Z Connelly, Abram Random NP-Complete problems have come under study as an important tool used in the analysis of optimization algorithms and help in our understanding of how to properly address issues of computational intractability. In this thesis, the Number Partition Problem and the Hamiltonian Cycle Problem are taken as representative NP-Complete classes. Numerical evidence is presented for a phase transition in the probability of solution when a modified Lévy-Stable distribution is used in instance creation for each. Numerical evidence is presented that show hard random instances exist near the critical threshold for the Hamiltonian Cycle problem. A choice of order parameter for the Number Partition Problem’s phase transition is also given. Finding Hamiltonian Cycles in Erdös-Rényi random graphs is well known to have almost sure polynomial time algorithms, even near the critical threshold. To the author’s knowledge, the graph ensemble presented is the first candidate, without specific graph structure built in, to generate graphs whose Hamiltonicity is intrinsically hard to determine. Random graphs are chosen via their degree sequence generated from a discretized form of Lévy-Stable distributions. Graphs chosen from this distribution still show a phase transition and appear to have a pickup in search cost for the algorithms considered. Search cost is highly dependent on the particular algorithm used and the graph ensemble is presented only as a potential graph ensemble to generate intrinsically hard graphs that are difficult to test for Hamiltonicity. Number Partition Problem instances are created by choosing each element in the list from a modified Lévy-Stable distribution. The Number Partition Problem has no known good approximation algorithms and so only numerical evidence to show the phase transition is provided without considerable focus on pickup in search cost for the solvers used. The failure of current approximation algorithms and potential candidate approximation algorithms are discussed. http://hdl.handle.net/10023/2124 Abstract: This thesis establishes a framework for facial feature detection and human face movement tracking. Statistical models of shape and appearance are built to represent the human face structure and interpret target images of human faces. The approach is a patch-based method derived from an earlier proposed method, the constrained local model (CLM) [1] algorithm. In order to increase the ability to track face movements with large head rotations, a 3D shape model is used in the system. And multiple texture models from different viewpoints are used to model the appearance. During fitting or tracking, the current estimate of pose (shape coordinates) is used to select the appropriate texture model. The algorithm uses the shape model and a texture model to generate a set of region template detectors. A search is then performed in the global pose / shape space using these detectors. Different optimisation frameworks are used in the implementation. The training images are created by rendering expressive 3D face models with different scales, rotations, expressions, brightness, etc. Experimental results are demonstrated by fitting the model to image sequences with large head rotations to evaluate the performance of the algorithm. To evaluate the stability and selection of factors of the algorithm, more experiments are carried out. The results show that the proposed 3D constrained local model algorithm improves the performance of the original CLM algorithm for videos with large out-of-plane head rotations. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10023/2124 2010-01-01T00:00:00Z Yu, Meng This thesis establishes a framework for facial feature detection and human face movement tracking. Statistical models of shape and appearance are built to represent the human face structure and interpret target images of human faces. The approach is a patch-based method derived from an earlier proposed method, the constrained local model (CLM) [1] algorithm. In order to increase the ability to track face movements with large head rotations, a 3D shape model is used in the system. And multiple texture models from different viewpoints are used to model the appearance. During fitting or tracking, the current estimate of pose (shape coordinates) is used to select the appropriate texture model. The algorithm uses the shape model and a texture model to generate a set of region template detectors. A search is then performed in the global pose / shape space using these detectors. Different optimisation frameworks are used in the implementation. The training images are created by rendering expressive 3D face models with different scales, rotations, expressions, brightness, etc. Experimental results are demonstrated by fitting the model to image sequences with large head rotations to evaluate the performance of the algorithm. To evaluate the stability and selection of factors of the algorithm, more experiments are carried out. The results show that the proposed 3D constrained local model algorithm improves the performance of the original CLM algorithm for videos with large out-of-plane head rotations. http://hdl.handle.net/10023/2100 Abstract: Backtracking CSP solvers provide a powerful framework for search and reasoning. The aim of constraint learning is increase global reasoning power by learning new constraints to boost reasoning and hopefully reduce search effort. In this thesis constraint learning is developed in several ways to make it faster and more powerful. First, lazy explanation generation is introduced, where explanations are generated as needed rather than continuously during propagation. This technique is shown to be effective is reducing the number of explanations generated substantially and consequently reducing the amount of time taken to complete a search, over a wide selection of benchmarks. Second, a series of experiments are undertaken investigating constraint forgetting, where constraints are discarded to avoid time and space costs associated with learning new constraints becoming too large. A major empirical investigation into the overheads introduced by unbounded constraint learning in CSP is conducted. This is the first such study in either CSP or SAT. Two significant results are obtained. The first is that typically a small percentage of learnt constraints do most propagation. While this is conventional wisdom, it has not previously been the subject of empirical study. The second is that even constraints that do no effective propagation can incur significant time overheads. Finally, the use of forgetting techniques from the literature is shown to significantly improve the performance of modern learning CSP solvers, contradicting some previous research. Finally, learning is generalised to use disjunctions of arbitrary constraints, where before only disjunctions of assignments and disassignments have been used in practice (g-nogood learning). The details of the implementation undertaken show that major gains in expressivity are available, and this is confirmed by a proof that it can save an exponential amount of search in practice compared with g-nogood learning. Experiments demonstrate the promise of the technique. Sun, 01 May 2011 00:00:00 GMT http://hdl.handle.net/10023/2100 2011-05-01T00:00:00Z Moore, Neil C.A. Backtracking CSP solvers provide a powerful framework for search and reasoning. The aim of constraint learning is increase global reasoning power by learning new constraints to boost reasoning and hopefully reduce search effort. In this thesis constraint learning is developed in several ways to make it faster and more powerful. First, lazy explanation generation is introduced, where explanations are generated as needed rather than continuously during propagation. This technique is shown to be effective is reducing the number of explanations generated substantially and consequently reducing the amount of time taken to complete a search, over a wide selection of benchmarks. Second, a series of experiments are undertaken investigating constraint forgetting, where constraints are discarded to avoid time and space costs associated with learning new constraints becoming too large. A major empirical investigation into the overheads introduced by unbounded constraint learning in CSP is conducted. This is the first such study in either CSP or SAT. Two significant results are obtained. The first is that typically a small percentage of learnt constraints do most propagation. While this is conventional wisdom, it has not previously been the subject of empirical study. The second is that even constraints that do no effective propagation can incur significant time overheads. Finally, the use of forgetting techniques from the literature is shown to significantly improve the performance of modern learning CSP solvers, contradicting some previous research. Finally, learning is generalised to use disjunctions of arbitrary constraints, where before only disjunctions of assignments and disassignments have been used in practice (g-nogood learning). The details of the implementation undertaken show that major gains in expressivity are available, and this is confirmed by a proof that it can save an exponential amount of search in practice compared with g-nogood learning. Experiments demonstrate the promise of the technique. http://hdl.handle.net/10023/2095 Abstract: Robotics has been the subject of academic study from as early as 1948. For much of this time, study has focused on very specific applications in very well controlled environments. For example, the first commercial robots (1961) were introduced in order to improve the efficiency of production lines. The tasks undertaken by these robots were simple, and all that was required of a control algorithm was speed, repetitiveness and reliability in these environments. Now however, robots are being used to move around autonomously in increasingly unpredictable environments, and the need for robotic control algorithms that can successfully react to such conditions is ever increasing. In addition to this there is an ever-increasing array of robots available, the control algorithms for which are often incompatible. This can result in extensive redesign and large sections of code being re-written for use on different architectures. The thesis presented here is that a new generic approach can be created that provides robust high quality smooth paths and time-optimal path tracking to substantially increase applicability and efficiency of autonomous motion plans. The control system developed to support this thesis is capable of producing high quality smooth paths, and following these paths to a high level of accuracy in a robust and near time-optimal manner. The system can control a variety of robots in environments that contain 2D obstacles of various shapes and sizes. The system is also resilient to sensor error, spatial drift, and wheel-slip. In achieving the above, this system provides previously unavailable functionality by generically creating and tracking high quality paths so that only minor and clear adjustments are required between different robots and also be being capable of operating in environments that contain high levels of perturbation. The system is comprised of five separate novel component algorithms in order to cater for five different motion challenges facing modern robots. Each algorithm provides guaranteed functionality that has previously been unavailable in respect to its challenges. The challenges are: high quality smooth movement to reach n-dimensional goals in regions without obstacles, the navigation of 2D obstacles with guaranteed completeness, high quality smooth movement for ground robots carrying out 2D obstacle navigation, near time-optimal path tracking, and finally, effective wheel-slip detection and compensation. In meeting these challenges the algorithms have tackled adherence to non-holonomic constraints, applicability to a wide range of robots and tasks, fast real-time creation of paths and controls, sensor error compensation, and compensation for perturbation. This thesis presents each of the above algorithms individually. It is shown that existing methods are unable to produce the results provided by this thesis, before detailing the operation of each algorithm. The methodology employed is varied in accordance with each of the five core challenges. However, a common element of methodology throughout the thesis is that of gradient descent within a new type of potential field, which is dynamic and capable of the simultaneous creation of high-quality paths and the controls required to execute them. By relating global to local considerations through subgoals, this methodology (combined with other elements) is shown to be fully capable of achieving the aims of the thesis. It is concluded that the produced system represents a novel and significant contribution as there is no other system (to the author’s knowledge) that provides all of the functionality given. For each component algorithm there are many control systems that provide one or more of its features, but none that are capable of all of the features. Applications for this work are wide ranging as it is comprised of five component algorithms each applicable in their own right. For example, high quality smooth paths may be created and followed in any dimensionality of space if time optimality and obstacle avoidance are not required. Broadly speaking, and in summary, applications are to ground-based robotics in the areas of smooth path planning, time optimal travel, and compensation for unpredictable perturbation. Wed, 30 Nov 2011 00:00:00 GMT http://hdl.handle.net/10023/2095 2011-11-30T00:00:00Z Bott, M. P. Robotics has been the subject of academic study from as early as 1948. For much of this time, study has focused on very specific applications in very well controlled environments. For example, the first commercial robots (1961) were introduced in order to improve the efficiency of production lines. The tasks undertaken by these robots were simple, and all that was required of a control algorithm was speed, repetitiveness and reliability in these environments. Now however, robots are being used to move around autonomously in increasingly unpredictable environments, and the need for robotic control algorithms that can successfully react to such conditions is ever increasing. In addition to this there is an ever-increasing array of robots available, the control algorithms for which are often incompatible. This can result in extensive redesign and large sections of code being re-written for use on different architectures. The thesis presented here is that a new generic approach can be created that provides robust high quality smooth paths and time-optimal path tracking to substantially increase applicability and efficiency of autonomous motion plans. The control system developed to support this thesis is capable of producing high quality smooth paths, and following these paths to a high level of accuracy in a robust and near time-optimal manner. The system can control a variety of robots in environments that contain 2D obstacles of various shapes and sizes. The system is also resilient to sensor error, spatial drift, and wheel-slip. In achieving the above, this system provides previously unavailable functionality by generically creating and tracking high quality paths so that only minor and clear adjustments are required between different robots and also be being capable of operating in environments that contain high levels of perturbation. The system is comprised of five separate novel component algorithms in order to cater for five different motion challenges facing modern robots. Each algorithm provides guaranteed functionality that has previously been unavailable in respect to its challenges. The challenges are: high quality smooth movement to reach n-dimensional goals in regions without obstacles, the navigation of 2D obstacles with guaranteed completeness, high quality smooth movement for ground robots carrying out 2D obstacle navigation, near time-optimal path tracking, and finally, effective wheel-slip detection and compensation. In meeting these challenges the algorithms have tackled adherence to non-holonomic constraints, applicability to a wide range of robots and tasks, fast real-time creation of paths and controls, sensor error compensation, and compensation for perturbation. This thesis presents each of the above algorithms individually. It is shown that existing methods are unable to produce the results provided by this thesis, before detailing the operation of each algorithm. The methodology employed is varied in accordance with each of the five core challenges. However, a common element of methodology throughout the thesis is that of gradient descent within a new type of potential field, which is dynamic and capable of the simultaneous creation of high-quality paths and the controls required to execute them. By relating global to local considerations through subgoals, this methodology (combined with other elements) is shown to be fully capable of achieving the aims of the thesis. It is concluded that the produced system represents a novel and significant contribution as there is no other system (to the author’s knowledge) that provides all of the functionality given. For each component algorithm there are many control systems that provide one or more of its features, but none that are capable of all of the features. Applications for this work are wide ranging as it is comprised of five component algorithms each applicable in their own right. For example, high quality smooth paths may be created and followed in any dimensionality of space if time optimality and obstacle avoidance are not required. Broadly speaking, and in summary, applications are to ground-based robotics in the areas of smooth path planning, time optimal travel, and compensation for unpredictable perturbation. http://hdl.handle.net/10023/1899 Abstract: This work starts from the proposition that it is beneficial to conserve communication energy in Wireless Sensor Networks (WSNs). For WSNs there is an added incentive for energy-efficient communication. The power supply of a sensor is often finite and small. Replenishing the power may be impractical and is likely to be costly. Wireless Sensor Networks are an important area of research. Data about the physical environment may be collected from hostile or friendly environments. Data is then transmitted to a destination without the need for communication cables. There are power and resource constraints upon WSNs, in addition WSN networks are often application specific. Different applications will often have different requirements. Further, WSNs are a shared medium system. The features of the MAC (Medium Access Control) protocol together with the application behaviour shape the communication states of the node. As each of these states have different power requirements the MAC protocol impacts upon the operation and power consumption efficiency. This work focuses on the development of an energy conservation protocol for WSNs where direct communication between sources and a base station is feasible. Whilst the multi-hop approach has been regarded as the underlying communication paradigm in WSNs, there are some scenarios where direct communication is applicable and a significant amount of communication energy can be saved. The Power & Reliability Aware Protocol has been developed. Its main objectives are to provide efficient data communication by means of energy conservation without sacrificing required reliability. This has been achieved by using direct communication, adaptive power adaptation and intelligent scheduling. The results of simulations illustrate the significance of communication energy and adaptive transmission. The relationship between Received Signal Strength Indicator (RSSI) and Packet Reception Rate (PRR) metrics is established and used to identify when power adaptation is required. The experimental results demonstrate an optimal region where lower power can be used without further reduction in the PRR. Communication delays depend upon the packet size whilst two-way propagation delay is very small. Accurate scheduling is achieved through monitoring the clock drift. A set of experiments were carried out to study benefits of direct vs. multi-hop communication. Significant transmitting current can be conserved if the direct communication is used. PoRAP is compared to Sensor-MAC (S-MAC), Berkeley-MAC (B-MAC) and Carrier Sense Multiple Access (CSMA). Parameter settings used in the Great Duck Island (GDI) a production habitat monitoring WSNs were applied. PoRAP consumes the least amount of energy. Thu, 23 Jun 2011 00:00:00 GMT http://hdl.handle.net/10023/1899 2011-06-23T00:00:00Z Khemapech, Ittipong This work starts from the proposition that it is beneficial to conserve communication energy in Wireless Sensor Networks (WSNs). For WSNs there is an added incentive for energy-efficient communication. The power supply of a sensor is often finite and small. Replenishing the power may be impractical and is likely to be costly. Wireless Sensor Networks are an important area of research. Data about the physical environment may be collected from hostile or friendly environments. Data is then transmitted to a destination without the need for communication cables. There are power and resource constraints upon WSNs, in addition WSN networks are often application specific. Different applications will often have different requirements. Further, WSNs are a shared medium system. The features of the MAC (Medium Access Control) protocol together with the application behaviour shape the communication states of the node. As each of these states have different power requirements the MAC protocol impacts upon the operation and power consumption efficiency. This work focuses on the development of an energy conservation protocol for WSNs where direct communication between sources and a base station is feasible. Whilst the multi-hop approach has been regarded as the underlying communication paradigm in WSNs, there are some scenarios where direct communication is applicable and a significant amount of communication energy can be saved. The Power & Reliability Aware Protocol has been developed. Its main objectives are to provide efficient data communication by means of energy conservation without sacrificing required reliability. This has been achieved by using direct communication, adaptive power adaptation and intelligent scheduling. The results of simulations illustrate the significance of communication energy and adaptive transmission. The relationship between Received Signal Strength Indicator (RSSI) and Packet Reception Rate (PRR) metrics is established and used to identify when power adaptation is required. The experimental results demonstrate an optimal region where lower power can be used without further reduction in the PRR. Communication delays depend upon the packet size whilst two-way propagation delay is very small. Accurate scheduling is achieved through monitoring the clock drift. A set of experiments were carried out to study benefits of direct vs. multi-hop communication. Significant transmitting current can be conserved if the direct communication is used. PoRAP is compared to Sensor-MAC (S-MAC), Berkeley-MAC (B-MAC) and Carrier Sense Multiple Access (CSMA). Parameter settings used in the Great Duck Island (GDI) a production habitat monitoring WSNs were applied. PoRAP consumes the least amount of energy. http://hdl.handle.net/10023/1844 Abstract: This thesis presents a scalable service-oriented architecture for the demand-driven deployment of location-neutral software services, using an end-to-end or ‘holistic’ approach to address identified shortcomings of the traditional Web Services model. The architecture presents a multi-endpoint Web Service environment which abstracts over Web Service location and technology and enables the dynamic provision of highly-available Web Services. The model describes mechanisms which provide a framework within which Web Services can be reliably addressed, bound to, and utilized, at any time and from any location. The presented model eases the task of providing a Web Service by consuming deployment and management tasks. It eases the development of consumer agent applications by letting developers program against what a service does, not where it is or whether it is currently deployed. It extends the platform-independent ethos of Web Services by providing deployment mechanisms which can be used independent of implementation and deployment technologies. Crucially, it maintains the Web Service goal of universal interoperability, preserving each actor’s view upon the system so that existing Service Consumers and Service Providers can participate without any modifications to provider agent or consumer agent application code. Lastly, the model aims to enable the efficient consumption of hosting resources by providing mechanisms to dynamically apply and reclaim resources based upon measured consumer demand. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10023/1844 2010-01-01T00:00:00Z MacInnis, Robert F. This thesis presents a scalable service-oriented architecture for the demand-driven deployment of location-neutral software services, using an end-to-end or ‘holistic’ approach to address identified shortcomings of the traditional Web Services model. The architecture presents a multi-endpoint Web Service environment which abstracts over Web Service location and technology and enables the dynamic provision of highly-available Web Services. The model describes mechanisms which provide a framework within which Web Services can be reliably addressed, bound to, and utilized, at any time and from any location. The presented model eases the task of providing a Web Service by consuming deployment and management tasks. It eases the development of consumer agent applications by letting developers program against what a service does, not where it is or whether it is currently deployed. It extends the platform-independent ethos of Web Services by providing deployment mechanisms which can be used independent of implementation and deployment technologies. Crucially, it maintains the Web Service goal of universal interoperability, preserving each actor’s view upon the system so that existing Service Consumers and Service Providers can participate without any modifications to provider agent or consumer agent application code. Lastly, the model aims to enable the efficient consumption of hosting resources by providing mechanisms to dynamically apply and reclaim resources based upon measured consumer demand. http://hdl.handle.net/10023/1718 Abstract: Variable symmetries in constraint satisfaction problems can be broken by adding lexicographic ordering constraints. Existing general methods of generating such sets of ordering constraints can produce a huge number of additional constraints. This adds an unacceptable overhead to the solving process. Methods exist by which this large set of constraints can be reduced to a much smaller set automatically, but their application is also prohibitively costly. In contrast, this thesis takes a bottom up approach to generating symmetry breaking constraints. This will involve examining some commonly-occurring families of mathematical groups and deriving a general formula to produce a minimal set of ordering constraints which are sufficient to break all of the symmetry that each group describes. In some cases it is known that there exists no manageable sized sets of constraints to break all symmetries. One example of this occurs with matrix row and column symmetries. In such cases, incomplete symmetry breaking has been used to great effect. Double lex is a commonly used incomplete symmetry breaking technique for row and column symmetries. This thesis also describes another similar method which compares favourably to double lex. The general formulae investigated are used as building blocks to generate small sets of ordering constraints for more complex groups, constructed by combining smaller groups. Through the utilisation of graph automorphism tools and the groups and permutations software GAP we provide a method of defining variable symmetries in a problem as a group. Where this group can be described as the product of smaller groups, with known general formulae, we can construct a minimal set of ordering constraints for that problem automatically. In summary, this thesis provides the theoretical background necessary to apply efficient static symmetry breaking to constraint satisfaction problems. It also goes further, describing how this process can be automated to remove the necessity of having an expert CP practitioner, thus opening the field to a larger number of potential users. Sat, 01 Jan 2011 00:00:00 GMT http://hdl.handle.net/10023/1718 2011-01-01T00:00:00Z Grayland, Andrews Variable symmetries in constraint satisfaction problems can be broken by adding lexicographic ordering constraints. Existing general methods of generating such sets of ordering constraints can produce a huge number of additional constraints. This adds an unacceptable overhead to the solving process. Methods exist by which this large set of constraints can be reduced to a much smaller set automatically, but their application is also prohibitively costly. In contrast, this thesis takes a bottom up approach to generating symmetry breaking constraints. This will involve examining some commonly-occurring families of mathematical groups and deriving a general formula to produce a minimal set of ordering constraints which are sufficient to break all of the symmetry that each group describes. In some cases it is known that there exists no manageable sized sets of constraints to break all symmetries. One example of this occurs with matrix row and column symmetries. In such cases, incomplete symmetry breaking has been used to great effect. Double lex is a commonly used incomplete symmetry breaking technique for row and column symmetries. This thesis also describes another similar method which compares favourably to double lex. The general formulae investigated are used as building blocks to generate small sets of ordering constraints for more complex groups, constructed by combining smaller groups. Through the utilisation of graph automorphism tools and the groups and permutations software GAP we provide a method of defining variable symmetries in a problem as a group. Where this group can be described as the product of smaller groups, with known general formulae, we can construct a minimal set of ordering constraints for that problem automatically. In summary, this thesis provides the theoretical background necessary to apply efficient static symmetry breaking to constraint satisfaction problems. It also goes further, describing how this process can be automated to remove the necessity of having an expert CP practitioner, thus opening the field to a larger number of potential users. http://hdl.handle.net/10023/1702 Abstract: This dissertation highlights the importance of computer networking education and the challenges in engaging and educating students. An exploratory learning approach is discussed with reference to other learning models and taxonomies. It is felt that an exploratory learning approach to wireless networks improves student engagement and perceived educational value. In order to support exploratory learning and improve the effectiveness of computer networking education the WiFi Virtual Laboratory (WiFiVL) has been developed. This framework enables students to access a powerful network simulator without the barrier of learning a specialised systems programming language. The WiFiVL has been designed to provide “anytime anywhere” access to a self-paced or guided exploratory learning environment. The initial framework was designed to enable users to access a network simulator using an HTML form embedded in a web page. Users could construct a scenario wherein multiple wireless nodes were situated. Traffic links between the nodes were also specified using the form interface. The scenario is then translated into a portable format, a URL, and simulated using the WiFiVL framework detailed in this dissertation. The resulting simulation is played back to the user on a web page, via a Flash animation. This initial approach was extended to exploit the greater potential for interaction afforded by a Rich Internet Application (RIA), referred to as WiFiVL II. The dissertation also details the expansion of WiFiVL into the realm of 3-dimensional, immersive, virtual worlds. It is shown how these virtual worlds can be exploited to create an engaging and educational virtual laboratory for wireless networks. Throughout each development the supporting framework has been re-used and has proved capable of supporting multiple interfaces and views. Each of the implementations described in this dissertation has been evaluated with learners in undergraduate and postgraduate degrees at the University of St Andrews. The results validate the efficacy of a virtual laboratory approach for supporting exploratory learning for wireless networks. Tue, 30 Nov 2010 00:00:00 GMT http://hdl.handle.net/10023/1702 2010-11-30T00:00:00Z Sturgeon, Thomas This dissertation highlights the importance of computer networking education and the challenges in engaging and educating students. An exploratory learning approach is discussed with reference to other learning models and taxonomies. It is felt that an exploratory learning approach to wireless networks improves student engagement and perceived educational value. In order to support exploratory learning and improve the effectiveness of computer networking education the WiFi Virtual Laboratory (WiFiVL) has been developed. This framework enables students to access a powerful network simulator without the barrier of learning a specialised systems programming language. The WiFiVL has been designed to provide “anytime anywhere” access to a self-paced or guided exploratory learning environment. The initial framework was designed to enable users to access a network simulator using an HTML form embedded in a web page. Users could construct a scenario wherein multiple wireless nodes were situated. Traffic links between the nodes were also specified using the form interface. The scenario is then translated into a portable format, a URL, and simulated using the WiFiVL framework detailed in this dissertation. The resulting simulation is played back to the user on a web page, via a Flash animation. This initial approach was extended to exploit the greater potential for interaction afforded by a Rich Internet Application (RIA), referred to as WiFiVL II. The dissertation also details the expansion of WiFiVL into the realm of 3-dimensional, immersive, virtual worlds. It is shown how these virtual worlds can be exploited to create an engaging and educational virtual laboratory for wireless networks. Throughout each development the supporting framework has been re-used and has proved capable of supporting multiple interfaces and views. Each of the implementations described in this dissertation has been evaluated with learners in undergraduate and postgraduate degrees at the University of St Andrews. The results validate the efficacy of a virtual laboratory approach for supporting exploratory learning for wireless networks. http://hdl.handle.net/10023/1673 Abstract: In an orthogonally persistent programming system, data is treated in a manner independent of its persistence. This gives simpler semantics, allows the programmer to ignore details of long-term data storage and enables type checking protection mechanisms to operate over the entire lifetime of the data. The ultimate goal of persistent programming language research is to reduce the costs of producing software. The work presented in this thesis seeks to improve programmer productivity in the following ways: • by reducing the amount of code that has to be written to construct an application; • by increasing the reliability of the code written; and • by improving the programmer’s understanding of the persistent environment in which applications are constructed. Two programming techniques that may be used to pursue these goals in a persistent environment are type-safe linguistic reflection and hyper-programming. The first provides a mechanism by which the programmer can write generators that, when executed, produce new program representations. This allows the specification of programs that are highly generic yet depend in non-trivial ways on the types of the data on which they operate. Genericity promotes software reuse which in turn reduces the amount of new code that has to be written. Hyper-programming allows a source program to contain links to data items in the persistent store. This improves program reliability by allowing certain program checking to be performed earlier than is otherwise possible. It also reduces the amount of code written by permitting direct links to data in the place of textual descriptions. Both techniques contribute to the understanding of the persistent environment through supporting the implementation of store browsing tools and allowing source representations to be associated with all executable programs in the persistent store. This thesis describes in detail the structure of type-safe linguistic reflection and hyper-programming, their benefits in the persistent context, and a suite of programming tools that support reflective programming and hyper-programming. These tools may be used in conjunction to allow reflection over hyper-program representations. The implementation of the tools is described. Wed, 01 Jan 1992 00:00:00 GMT http://hdl.handle.net/10023/1673 1992-01-01T00:00:00Z Kirby, Graham Njal Cameron In an orthogonally persistent programming system, data is treated in a manner independent of its persistence. This gives simpler semantics, allows the programmer to ignore details of long-term data storage and enables type checking protection mechanisms to operate over the entire lifetime of the data. The ultimate goal of persistent programming language research is to reduce the costs of producing software. The work presented in this thesis seeks to improve programmer productivity in the following ways: • by reducing the amount of code that has to be written to construct an application; • by increasing the reliability of the code written; and • by improving the programmer’s understanding of the persistent environment in which applications are constructed. Two programming techniques that may be used to pursue these goals in a persistent environment are type-safe linguistic reflection and hyper-programming. The first provides a mechanism by which the programmer can write generators that, when executed, produce new program representations. This allows the specification of programs that are highly generic yet depend in non-trivial ways on the types of the data on which they operate. Genericity promotes software reuse which in turn reduces the amount of new code that has to be written. Hyper-programming allows a source program to contain links to data items in the persistent store. This improves program reliability by allowing certain program checking to be performed earlier than is otherwise possible. It also reduces the amount of code written by permitting direct links to data in the place of textual descriptions. Both techniques contribute to the understanding of the persistent environment through supporting the implementation of store browsing tools and allowing source representations to be associated with all executable programs in the persistent store. This thesis describes in detail the structure of type-safe linguistic reflection and hyper-programming, their benefits in the persistent context, and a suite of programming tools that support reflective programming and hyper-programming. These tools may be used in conjunction to allow reflection over hyper-program representations. The implementation of the tools is described. http://hdl.handle.net/10023/1350 Abstract: In this thesis we examine the relationship between hypersequent and some types of labelled sequent calculi for a subset of intermediate logics—logics between intuitionistic (Int), and classical logics—that have geometric Kripke semantics, which we call Int∗/Geo. We introduce a novel calculus for a fragment of first-order classical logic, which we call partially-shielded formulae (or PSF for short), that is adequate for expressing the semantic validity of formulae in Int∗/Geo, and apply techniques from correspondence theory to provide translations of hypersequents, simply labelled sequents and relational sequents (simply labelled sequents with relational formulae) into PSF. Using these translations, we show that hypersequents and simply labelled sequents for calculi in Int∗/Geo share the same models. We also use these translations to justify various techniques that we introduce for translating simply labelled sequents into relational sequents and vice versa. In particular, we introduce a technique called "transitive unfolding" for translating relational sequents into simply labelled sequents (and by extension, hypersequents) which preserves linear models in Int∗/Geo. We introduce syntactic translations between hypersequent calculi and simply labelled sequent calculi. We apply these translations to a novel hypersequent framework HG3ipm∗ for some logics in Int∗/Geo to obtain a corresponding simply labelled sequent framework LG3ipm∗, and to an existing simply labelled calculus for Int from the literature to obtain a novel hypersequent calculus for Int. We introduce methods for translating a simply labelled sequent calculus into a cor- responding relational calculus, and apply these methods to LG3ipm∗ to obtain a novel relational framework RG3ipm∗ that bears similarities to existing calculi from the literature. We use transitive unfolding to translate proofs in RG3ipm∗ into proofs in LG3ipm∗ and HG3ipm∗ with the communication rule, which corresponds to the semantic restriction to linear models. Fri, 04 Jun 2010 00:00:00 GMT http://hdl.handle.net/10023/1350 2010-06-04T00:00:00Z Rothenberg, Robert In this thesis we examine the relationship between hypersequent and some types of labelled sequent calculi for a subset of intermediate logics—logics between intuitionistic (Int), and classical logics—that have geometric Kripke semantics, which we call Int∗/Geo. We introduce a novel calculus for a fragment of first-order classical logic, which we call partially-shielded formulae (or PSF for short), that is adequate for expressing the semantic validity of formulae in Int∗/Geo, and apply techniques from correspondence theory to provide translations of hypersequents, simply labelled sequents and relational sequents (simply labelled sequents with relational formulae) into PSF. Using these translations, we show that hypersequents and simply labelled sequents for calculi in Int∗/Geo share the same models. We also use these translations to justify various techniques that we introduce for translating simply labelled sequents into relational sequents and vice versa. In particular, we introduce a technique called "transitive unfolding" for translating relational sequents into simply labelled sequents (and by extension, hypersequents) which preserves linear models in Int∗/Geo. We introduce syntactic translations between hypersequent calculi and simply labelled sequent calculi. We apply these translations to a novel hypersequent framework HG3ipm∗ for some logics in Int∗/Geo to obtain a corresponding simply labelled sequent framework LG3ipm∗, and to an existing simply labelled calculus for Int from the literature to obtain a novel hypersequent calculus for Int. We introduce methods for translating a simply labelled sequent calculus into a cor- responding relational calculus, and apply these methods to LG3ipm∗ to obtain a novel relational framework RG3ipm∗ that bears similarities to existing calculi from the literature. We use transitive unfolding to translate proofs in RG3ipm∗ into proofs in LG3ipm∗ and HG3ipm∗ with the communication rule, which corresponds to the semantic restriction to linear models. http://hdl.handle.net/10023/1295 Abstract: A Wireless Sensor Network (WSN) consists of a number of nodes, each typically having a small amount of non-replenishable energy. Some of the nodes have sensors, which may be used to gather environmental data. A common network abstraction used in WSNs is the (source, sink) architecture in which data is generated at one or more sources and sent to one or more sinks using wireless communication, possibly via intermediate nodes. In such systems, wireless communication is usually implemented using radio. Transmitting or receiving, even on a low power radio, is much more energy-expensive than other activities such as computation and consequently, the radio must be used judiciously to avoid unnecessary depletion of energy. Eventually, the loss of energy at each node will cause it to stop operating, resulting in the loss of data acquisition and data delivery. Whilst the loss of some nodes may be tolerable, albeit undesirable, the loss of certain critical nodes in a multi-hop routing environment may cause network partitions such that data may no longer be deliverable to sinks, reducing the usefulness of the network. This thesis presents a new heuristic known as node reliance and demonstrates its efficacy in prolonging the useful lifetime of WSNs. The node reliance heuristic attempts to keep as many sources and sinks connected for as long as possible. It achieves this using a reliance value that measures the degree to which a node is relied upon in routing data from sources to sinks. By forming routes that avoid high reliance nodes, the usefulness of the network may be extended. The hypothesis of this thesis is that the useful lifetime of a WSN may be improved by node reliance routing in which paths from sources to sinks avoid critical nodes where possible. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10023/1295 2010-01-01T00:00:00Z Boyd, Alan W. F. A Wireless Sensor Network (WSN) consists of a number of nodes, each typically having a small amount of non-replenishable energy. Some of the nodes have sensors, which may be used to gather environmental data. A common network abstraction used in WSNs is the (source, sink) architecture in which data is generated at one or more sources and sent to one or more sinks using wireless communication, possibly via intermediate nodes. In such systems, wireless communication is usually implemented using radio. Transmitting or receiving, even on a low power radio, is much more energy-expensive than other activities such as computation and consequently, the radio must be used judiciously to avoid unnecessary depletion of energy. Eventually, the loss of energy at each node will cause it to stop operating, resulting in the loss of data acquisition and data delivery. Whilst the loss of some nodes may be tolerable, albeit undesirable, the loss of certain critical nodes in a multi-hop routing environment may cause network partitions such that data may no longer be deliverable to sinks, reducing the usefulness of the network. This thesis presents a new heuristic known as node reliance and demonstrates its efficacy in prolonging the useful lifetime of WSNs. The node reliance heuristic attempts to keep as many sources and sinks connected for as long as possible. It achieves this using a reliance value that measures the degree to which a node is relied upon in routing data from sources to sinks. By forming routes that avoid high reliance nodes, the usefulness of the network may be extended. The hypothesis of this thesis is that the useful lifetime of a WSN may be improved by node reliance routing in which paths from sources to sinks avoid critical nodes where possible. http://hdl.handle.net/10023/973 Abstract: Constraint Programming is a powerful technique for solving large-scale combinatorial (optimisation) problems. However, it is often inaccessible to users without expert knowledge in the area, precluding the wide-spread use of Constraint Programming techniques. This thesis addresses this issue in three main contributions. First, we propose a simple ‘model-and-solve’ approach, consisting of a framework where the user formulates a solver-independent problem model, which is then automatically tailored to the input format of a selected constraint solver (a process similar to compiling a high-level modelling language to machine code). The solver is then executed on the input, solver, and solutions (if they exist) are returned to the user. This allows the user to formulate constraint models without requiring any particular background knowledge of the respective solver and its solving technique. Furthermore, since the framework can target several solvers, the user can explore different types of solvers. Second, we extend the tailoring process with model optimisations that can compensate for a wide selection of poor modelling choices that novices (and experts) in Constraint Programming often make and hence result in redundancies. The elimination of these redundancies by the proposed optimisation techniques can result in solving time speedups of over an order of magnitude, in both naive and expert models. Furthermore, the optimisations are particularly light-weight, adding negligible overhead to the overall translation process. The third contribution is the implementation of this framework in the tool TAILOR, that currently translates 2 different solver-independent modelling languages to 3 different solver formats and is freely available online. It performs almost all optimisation techniques that are proposed in this thesis and demonstrates its significance in our empirical analysis. In summary, this thesis presents a framework that facilitates modelling for both experts and novices: problems can be formulated in a clear, high-level fashion, without requiring any particular background knowledge about constraint solvers and their solving techniques, while (sometimes naturally occurring) redundancies in the model are eliminated for practically no additional cost, improving the respective model in solving performance by up to an order of magnitude. Fri, 01 Jan 2010 00:00:00 GMT http://hdl.handle.net/10023/973 2010-01-01T00:00:00Z Rendl, Andrea Constraint Programming is a powerful technique for solving large-scale combinatorial (optimisation) problems. However, it is often inaccessible to users without expert knowledge in the area, precluding the wide-spread use of Constraint Programming techniques. This thesis addresses this issue in three main contributions. First, we propose a simple ‘model-and-solve’ approach, consisting of a framework where the user formulates a solver-independent problem model, which is then automatically tailored to the input format of a selected constraint solver (a process similar to compiling a high-level modelling language to machine code). The solver is then executed on the input, solver, and solutions (if they exist) are returned to the user. This allows the user to formulate constraint models without requiring any particular background knowledge of the respective solver and its solving technique. Furthermore, since the framework can target several solvers, the user can explore different types of solvers. Second, we extend the tailoring process with model optimisations that can compensate for a wide selection of poor modelling choices that novices (and experts) in Constraint Programming often make and hence result in redundancies. The elimination of these redundancies by the proposed optimisation techniques can result in solving time speedups of over an order of magnitude, in both naive and expert models. Furthermore, the optimisations are particularly light-weight, adding negligible overhead to the overall translation process. The third contribution is the implementation of this framework in the tool TAILOR, that currently translates 2 different solver-independent modelling languages to 3 different solver formats and is freely available online. It performs almost all optimisation techniques that are proposed in this thesis and demonstrates its significance in our empirical analysis. In summary, this thesis presents a framework that facilitates modelling for both experts and novices: problems can be formulated in a clear, high-level fashion, without requiring any particular background knowledge about constraint solvers and their solving techniques, while (sometimes naturally occurring) redundancies in the model are eliminated for practically no additional cost, improving the respective model in solving performance by up to an order of magnitude. http://hdl.handle.net/10023/933 Abstract: Whilst results from Structural Proof Theory can be couched in many formalisms, it is the sequent calculus which is the most amenable of the formalisms to metamathematical treatment. Constructive syntactic proofs are filled with bureaucratic details; rarely are all cases of a proof completed in the literature. Two intermediate results can be used to drastically reduce the amount of effort needed in proofs of Cut admissibility: Weakening and Invertibility. Indeed, whereas there are proofs of Cut admissibility which do not use Invertibility, Weakening is almost always necessary. Use of these results simply shifts the bureaucracy, however; Weakening and Invertibility, whilst more easy to prove, are still not trivial. We give a framework under which sequent calculi can be codified and analysed, which then allows us to prove various results: for a calculus to admit Weakening and for a rule to be invertible in a calculus. For the latter, even though many calculi are investigated, the general condition is simple and easily verified. The results have been applied to G3ip, G3cp, G3s, G3-LC and G4ip. Invertibility is important in another respect; that of proof-search. Should all rules in a calculus be invertible, then terminating root-first proof search gives a decision procedure for formulae without the need for back-tracking. To this end, we present some results about the manipulation of rule sets. It is shown that the transformations do not affect the expressiveness of the calculus, yet may render more rules invertible. These results can guide the design of efficient calculi. When using interactive proof assistants, every case of a proof, however complex, must be addressed and proved before one can declare the result formalised. To do this in a human readable way adds a further layer of complexity; most proof assistants give output which is only legible to a skilled user of that proof assistant. We give human-readable formalisations of Cut admissibility for G3cp and G3ip, Contraction admissibility for G4ip and Craig's Interpolation Theorem for G3i using the Isar vernacular of Isabelle. We also formalise the new invertibility results, in part using the package for reasoning about first-order languages, Nominal Isabelle. Examples are given showing the effectiveness of the formalisation. The formal proof of invertibility using the new methods is drastically shorter than the traditional, direct method. Tue, 01 Jun 2010 00:00:00 GMT http://hdl.handle.net/10023/933 2010-06-01T00:00:00Z Chapman, Peter Whilst results from Structural Proof Theory can be couched in many formalisms, it is the sequent calculus which is the most amenable of the formalisms to metamathematical treatment. Constructive syntactic proofs are filled with bureaucratic details; rarely are all cases of a proof completed in the literature. Two intermediate results can be used to drastically reduce the amount of effort needed in proofs of Cut admissibility: Weakening and Invertibility. Indeed, whereas there are proofs of Cut admissibility which do not use Invertibility, Weakening is almost always necessary. Use of these results simply shifts the bureaucracy, however; Weakening and Invertibility, whilst more easy to prove, are still not trivial. We give a framework under which sequent calculi can be codified and analysed, which then allows us to prove various results: for a calculus to admit Weakening and for a rule to be invertible in a calculus. For the latter, even though many calculi are investigated, the general condition is simple and easily verified. The results have been applied to G3ip, G3cp, G3s, G3-LC and G4ip. Invertibility is important in another respect; that of proof-search. Should all rules in a calculus be invertible, then terminating root-first proof search gives a decision procedure for formulae without the need for back-tracking. To this end, we present some results about the manipulation of rule sets. It is shown that the transformations do not affect the expressiveness of the calculus, yet may render more rules invertible. These results can guide the design of efficient calculi. When using interactive proof assistants, every case of a proof, however complex, must be addressed and proved before one can declare the result formalised. To do this in a human readable way adds a further layer of complexity; most proof assistants give output which is only legible to a skilled user of that proof assistant. We give human-readable formalisations of Cut admissibility for G3cp and G3ip, Contraction admissibility for G4ip and Craig's Interpolation Theorem for G3i using the Isar vernacular of Isabelle. We also formalise the new invertibility results, in part using the package for reasoning about first-order languages, Nominal Isabelle. Examples are given showing the effectiveness of the formalisation. The formal proof of invertibility using the new methods is drastically shorter than the traditional, direct method. http://hdl.handle.net/10023/930 Abstract: System deployment projects are extremely complex and with more and more organisations now choosing to configure and deploy off-the-shelf systems, the project teams are presented with new challenges. The aim of this study was to gain an understanding of the issues faced during such configuration and deployment projects and see if support could be provided. A year long observational study of one of these projects was carried. While it was initially assumed that it would be technical issues related to the system’s configuration that would be the primary problems, the study revealed communication issues to be at the heart of a large number of the issues. Online social networks such as Facebook are extremely popular, allowing users to stay in touch with large numbers of distributed people. Private social network sites were applied to projects to see if they could replicate the benefits the sites provide and support project communications. A social network site was created for both a distributed research project and an administrative systems project and their use observed. Statistical data on the use of the sites and qualitative feedback from users is presented to assess the viability of the approach. The experiments showed social network sites to have many benefits when used as a complementary mechanism to traditional channels for project communications. It is clear however, that social network sites cannot solve all the problems projects may encounter. If the use of a site is to be a success it is vital it gains a critical mass of users. The approach taken to the site’s configuration and introduction will be hugely influential in its success. In order to choose the right approach a clear understanding of what the project’s communication needs are and the possible uses of the site is needed. A process of configuration and development with a small group of potential users is recommended to ensure it is as user friendly as possible before going live to a large user base. Wed, 23 Jun 2010 00:00:00 GMT http://hdl.handle.net/10023/930 2010-06-23T00:00:00Z Harvey, Natalie System deployment projects are extremely complex and with more and more organisations now choosing to configure and deploy off-the-shelf systems, the project teams are presented with new challenges. The aim of this study was to gain an understanding of the issues faced during such configuration and deployment projects and see if support could be provided. A year long observational study of one of these projects was carried. While it was initially assumed that it would be technical issues related to the system’s configuration that would be the primary problems, the study revealed communication issues to be at the heart of a large number of the issues. Online social networks such as Facebook are extremely popular, allowing users to stay in touch with large numbers of distributed people. Private social network sites were applied to projects to see if they could replicate the benefits the sites provide and support project communications. A social network site was created for both a distributed research project and an administrative systems project and their use observed. Statistical data on the use of the sites and qualitative feedback from users is presented to assess the viability of the approach. The experiments showed social network sites to have many benefits when used as a complementary mechanism to traditional channels for project communications. It is clear however, that social network sites cannot solve all the problems projects may encounter. If the use of a site is to be a success it is vital it gains a critical mass of users. The approach taken to the site’s configuration and introduction will be hugely influential in its success. In order to choose the right approach a clear understanding of what the project’s communication needs are and the possible uses of the site is needed. A process of configuration and development with a small group of potential users is recommended to ensure it is as user friendly as possible before going live to a large user base. http://hdl.handle.net/10023/926 Abstract: This thesis investigates the application of autonomic management to a distributed storage system. Effects on performance and resource consumption were measured in experiments, which were carried out in a local area test-bed. The experiments were conducted with components of one specific distributed storage system, but seek to be applicable to a wide range of such systems, in particular those exposed to varying conditions. The perceived characteristics of distributed storage systems depend on their configuration parameters and on various dynamic conditions. For a given set of conditions, one specific configuration may be better than another with respect to measures such as resource consumption and performance. Here, configuration parameter values were set dynamically and the results compared with a static configuration. It was hypothesised that under non-changing conditions this would allow the system to converge on a configuration that was more suitable than any that could be set a priori. Furthermore, the system could react to a change in conditions by adopting a more appropriate configuration. Autonomic management was applied to the peer-to-peer (P2P) and data retrieval components of ASA, a distributed storage system. The effects were measured experimentally for various workload and churn patterns. The management policies and mechanisms were implemented using a generic autonomic management framework developed during this work. The motivation for both groups of experiments was to test management policies with the objective to avoid unsatisfactory situations with respect to resource consumption and performance. Such unsatisfactory situations occur when either the P2P layer or the data retrieval mechanism is configured statically. In a statically configured P2P system two unsatisfactory situations can be identified. The first arises when the frequency with which P2P node states are verified is low and membership churn is high. The P2P node state becomes inaccurate due to a high membership churn, leading to errors during the routing process and a reduction in performance. In this situation it is desirable to increase the frequency to increase P2P state accuracy. The converse situation arises when the frequency is high and churn is low. In this situation network resources are used unnecessarily, which may also reduce performance, making it desirable to decrease the frequency. In ASA’s data retrieval mechanism similar unsatisfactory situations can be identified with respect to the degree of concurrency (DOC). The DOC controls the eagerness with which multiple redundant replicas are retrieved. An unsatisfactory situation arises when the DOC is low and there is a large variation in the times taken to retrieve replicas. In this situation it is desirable to increase the DOC, because by retrieving more replicas in parallel a result can be returned to the user sooner. The converse situation arises when the DOC is high, there is little variation in retrieval time and there is a network bottleneck close to the requesting client. In this situation it is desirable to decrease the DOC, since the low variation removes any benefit in parallel retrieval, and the bottleneck means that decreasing parallelism reduces both bandwidth consumption and elapsed time for the user. The experimental evaluations of autonomic management show promising results, and suggest several future research topics. These include optimisations of the managed mechanisms, alternative management policies, different evaluation methods, and the application of developed management mechanisms to other facets of a distributed storage system. The findings of this thesis could be exploited in building other distributed storage systems that focus on harnessing storage on user workstations, since these are particularly likely to be exposed to varying, unpredictable conditions. Wed, 23 Jun 2010 00:00:00 GMT http://hdl.handle.net/10023/926 2010-06-23T00:00:00Z Tauber, Markus This thesis investigates the application of autonomic management to a distributed storage system. Effects on performance and resource consumption were measured in experiments, which were carried out in a local area test-bed. The experiments were conducted with components of one specific distributed storage system, but seek to be applicable to a wide range of such systems, in particular those exposed to varying conditions. The perceived characteristics of distributed storage systems depend on their configuration parameters and on various dynamic conditions. For a given set of conditions, one specific configuration may be better than another with respect to measures such as resource consumption and performance. Here, configuration parameter values were set dynamically and the results compared with a static configuration. It was hypothesised that under non-changing conditions this would allow the system to converge on a configuration that was more suitable than any that could be set a priori. Furthermore, the system could react to a change in conditions by adopting a more appropriate configuration. Autonomic management was applied to the peer-to-peer (P2P) and data retrieval components of ASA, a distributed storage system. The effects were measured experimentally for various workload and churn patterns. The management policies and mechanisms were implemented using a generic autonomic management framework developed during this work. The motivation for both groups of experiments was to test management policies with the objective to avoid unsatisfactory situations with respect to resource consumption and performance. Such unsatisfactory situations occur when either the P2P layer or the data retrieval mechanism is configured statically. In a statically configured P2P system two unsatisfactory situations can be identified. The first arises when the frequency with which P2P node states are verified is low and membership churn is high. The P2P node state becomes inaccurate due to a high membership churn, leading to errors during the routing process and a reduction in performance. In this situation it is desirable to increase the frequency to increase P2P state accuracy. The converse situation arises when the frequency is high and churn is low. In this situation network resources are used unnecessarily, which may also reduce performance, making it desirable to decrease the frequency. In ASA’s data retrieval mechanism similar unsatisfactory situations can be identified with respect to the degree of concurrency (DOC). The DOC controls the eagerness with which multiple redundant replicas are retrieved. An unsatisfactory situation arises when the DOC is low and there is a large variation in the times taken to retrieve replicas. In this situation it is desirable to increase the DOC, because by retrieving more replicas in parallel a result can be returned to the user sooner. The converse situation arises when the DOC is high, there is little variation in retrieval time and there is a network bottleneck close to the requesting client. In this situation it is desirable to decrease the DOC, since the low variation removes any benefit in parallel retrieval, and the bottleneck means that decreasing parallelism reduces both bandwidth consumption and elapsed time for the user. The experimental evaluations of autonomic management show promising results, and suggest several future research topics. These include optimisations of the managed mechanisms, alternative management policies, different evaluation methods, and the application of developed management mechanisms to other facets of a distributed storage system. The findings of this thesis could be exploited in building other distributed storage systems that focus on harnessing storage on user workstations, since these are particularly likely to be exposed to varying, unpredictable conditions. http://hdl.handle.net/10023/923 Abstract: This dissertation presents a framework which supports a group-based exploratory approach to learning and integrates 3D gaming methods and technologies with an institutional learning environment. This provides learners with anytime-anywhere access to interactive learning materials, thereby supporting a self paced and personalised approach to learning. A simulation environment based on real world data has been developed, with a computer games methodology adopted as the means by which users are able to progress through the system. Within a virtual setting users, or groups of users, are faced with a series of dynamic challenges with which they engage until such time as they have shown a certain level of competence. Once a series of domain specific objectives have been met, users are able to progress forward to the next level of the simulation. Through the use of Internet and 3D visualisation technologies, an excavation simulator has been developed which provides the opportunity for students to engage in a virtual excavation project, applying their knowledge and reflecting on the outcomes of their decisions. The excavation simulator enhances the student learning experience by providing opportunities for students to engage with the archaeological excavation process in a customisable, virtual environment. Not only does this provide students with an opportunity to put some of the theories they are familiar with into practice, but it also allows for archaeology courses to place a greater emphasis on the practical application of knowledge that occurs during the excavation process. Laconia Acropolis Virtual Archaeology (LAVA) is a co-operative exploratory learning environment that addresses the need for students to engage with archaeological excavation scenarios. By leveraging the immersive nature of gaming technologies and 3D multi-user virtual environments (MUVEs), LAVA facilitates the adoption of exploratory learning practices in environments which have previously been inaccessible due to barriers of space, time or cost. Wed, 23 Jun 2010 00:00:00 GMT http://hdl.handle.net/10023/923 2010-06-23T00:00:00Z Getchell, Kristoffer M. This dissertation presents a framework which supports a group-based exploratory approach to learning and integrates 3D gaming methods and technologies with an institutional learning environment. This provides learners with anytime-anywhere access to interactive learning materials, thereby supporting a self paced and personalised approach to learning. A simulation environment based on real world data has been developed, with a computer games methodology adopted as the means by which users are able to progress through the system. Within a virtual setting users, or groups of users, are faced with a series of dynamic challenges with which they engage until such time as they have shown a certain level of competence. Once a series of domain specific objectives have been met, users are able to progress forward to the next level of the simulation. Through the use of Internet and 3D visualisation technologies, an excavation simulator has been developed which provides the opportunity for students to engage in a virtual excavation project, applying their knowledge and reflecting on the outcomes of their decisions. The excavation simulator enhances the student learning experience by providing opportunities for students to engage with the archaeological excavation process in a customisable, virtual environment. Not only does this provide students with an opportunity to put some of the theories they are familiar with into practice, but it also allows for archaeology courses to place a greater emphasis on the practical application of knowledge that occurs during the excavation process. Laconia Acropolis Virtual Archaeology (LAVA) is a co-operative exploratory learning environment that addresses the need for students to engage with archaeological excavation scenarios. By leveraging the immersive nature of gaming technologies and 3D multi-user virtual environments (MUVEs), LAVA facilitates the adoption of exploratory learning practices in environments which have previously been inaccessible due to barriers of space, time or cost. http://hdl.handle.net/10023/763 Abstract: The ability to synthesise the effects of ageing in human faces has numerous uses from aiding the search for missing people to improving recognition algorithms and aiding surgical planning. The principal contribution of this thesis is a novel method for synthesising the visual effects of facial ageing using a training set of three-dimensional scans to train a statistical ageing model. This data-base is constructed by fitting a statistical Face Model known as a Morphable Model to a set of two dimensional photographs of a set of subjects at different age points in their lives. We verify the effectiveness of this algorithm with both quantitative and psychological evaluation. Most ageing research has concentrated on building models using two-dimensional images. This has two major shortcomings, firstly some of the information related to shape change may be lost by the projection to two-dimensions; secondly the algorithms are very sensitive to even slight variations in pose and lighting. By using standard face-fitting methods to fit a statistical face model to the image we overcome these problems by reconstructing the lost shape information, and can use a model of physical rotations and light transfer to overcome the issues of pose and rotation. We show that the three-dimensional models captured by face-fitting offer an effective method of synthesising facial ageing. The second contribution is a new algorithm for ageing a face model based on Projection to Latent Structures also known as Partial Least Squares. This method attempts to separate the training set into a set of basis vectors that best explains the shape and colour changes related to ageing from those factors within the training set that are unrelated to ageing. We show that this method is more accurate than other linear techniques at producing a face model that resembles the individual at the target age and of producing a face image of the correct perceived age. The third contribution is a careful evaluation of three well known ageing methods. We use both quantitative evaluation to determine the accuracy of the ageing method, and perceptual evaluation to determine how well the model performs in terms of perceived age increase and also identity retention. We show that linear methods more accurately capture ageing and identity information if they are trained using an individualised model, and that ageing is more accurately captured if PLS is used to train the model. Mon, 30 Nov 2009 00:00:00 GMT http://hdl.handle.net/10023/763 2009-11-30T00:00:00Z Hunter, David W. The ability to synthesise the effects of ageing in human faces has numerous uses from aiding the search for missing people to improving recognition algorithms and aiding surgical planning. The principal contribution of this thesis is a novel method for synthesising the visual effects of facial ageing using a training set of three-dimensional scans to train a statistical ageing model. This data-base is constructed by fitting a statistical Face Model known as a Morphable Model to a set of two dimensional photographs of a set of subjects at different age points in their lives. We verify the effectiveness of this algorithm with both quantitative and psychological evaluation. Most ageing research has concentrated on building models using two-dimensional images. This has two major shortcomings, firstly some of the information related to shape change may be lost by the projection to two-dimensions; secondly the algorithms are very sensitive to even slight variations in pose and lighting. By using standard face-fitting methods to fit a statistical face model to the image we overcome these problems by reconstructing the lost shape information, and can use a model of physical rotations and light transfer to overcome the issues of pose and rotation. We show that the three-dimensional models captured by face-fitting offer an effective method of synthesising facial ageing. The second contribution is a new algorithm for ageing a face model based on Projection to Latent Structures also known as Partial Least Squares. This method attempts to separate the training set into a set of basis vectors that best explains the shape and colour changes related to ageing from those factors within the training set that are unrelated to ageing. We show that this method is more accurate than other linear techniques at producing a face model that resembles the individual at the target age and of producing a face image of the correct perceived age. The third contribution is a careful evaluation of three well known ageing methods. We use both quantitative evaluation to determine the accuracy of the ageing method, and perceptual evaluation to determine how well the model performs in terms of perceived age increase and also identity retention. We show that linear methods more accurately capture ageing and identity information if they are trained using an individualised model, and that ageing is more accurately captured if PLS is used to train the model. http://hdl.handle.net/10023/759 Abstract: Constraint satisfaction is a very well studied and fundamental artificial intelligence technique. Various forms of knowledge can be represented with constraints, and reasoning techniques from disparate fields can be encapsulated within constraint reasoning algorithms. However, problems involving uncertainty, or which have an adversarial nature (for example, games), are difficult to express and solve in the classical constraint satisfaction problem. This thesis is concerned with an extension to the classical problem: the Quantified Constraint Satisfaction Problem (QCSP). QCSP has recently attracted interest. In QCSP, quantifiers are allowed, facilitating the expression of uncertainty. I examine whether QCSP is a useful formalism. This divides into two questions: whether QCSP can be solved efficiently; and whether realistic problems can be represented in QCSP. In attempting to answer these questions, the main contributions of this thesis are the following: - the definition of two new notions of consistency; - four new constraint propagation algorithms (with eight variants in total), along with empirical evaluations; - two novel schemes to implement the pure value rule, which is able to simplify QCSP instances; - a new optimization algorithm for QCSP; - the integration of these algorithms and techniques into a solver named Queso; - and the modelling of the Connect 4 game, and of faulty job shop scheduling, in QCSP. These are set in context by a thorough review of the QCSP literature. Fri, 30 Nov 2007 00:00:00 GMT http://hdl.handle.net/10023/759 2007-11-30T00:00:00Z Nightingale, Peter Constraint satisfaction is a very well studied and fundamental artificial intelligence technique. Various forms of knowledge can be represented with constraints, and reasoning techniques from disparate fields can be encapsulated within constraint reasoning algorithms. However, problems involving uncertainty, or which have an adversarial nature (for example, games), are difficult to express and solve in the classical constraint satisfaction problem. This thesis is concerned with an extension to the classical problem: the Quantified Constraint Satisfaction Problem (QCSP). QCSP has recently attracted interest. In QCSP, quantifiers are allowed, facilitating the expression of uncertainty. I examine whether QCSP is a useful formalism. This divides into two questions: whether QCSP can be solved efficiently; and whether realistic problems can be represented in QCSP. In attempting to answer these questions, the main contributions of this thesis are the following: - the definition of two new notions of consistency; - four new constraint propagation algorithms (with eight variants in total), along with empirical evaluations; - two novel schemes to implement the pure value rule, which is able to simplify QCSP instances; - a new optimization algorithm for QCSP; - the integration of these algorithms and techniques into a solver named Queso; - and the modelling of the Connect 4 game, and of faulty job shop scheduling, in QCSP. These are set in context by a thorough review of the QCSP literature. http://hdl.handle.net/10023/564 Abstract: Programming resource-sensitive systems, such as real-time embedded systems, requires guaranteeing both the functional correctness of computations and also that time and space usage fits within constraints imposed by hardware limits or the environment. Functional programming languages have proved very good at meeting the former logical kind of guarantees but not the latter resource guarantees. This thesis contributes to demonstrate the applicability of functional programming in resource-sensitive systems with an automatic program analysis for obtaining guaranteed upper bounds on dynamic space usage of functional programs. Our analysis is developed for a core subset of Hume, a domain-specific functional language targeting resource-sensitive systems (Hammond et al. 2007), and presented as a type and effect system that builds on previous sized type systems (Hughes et al. 1996, Chin and Khoo 2001) and effect systems for costs (Dornic et al. 1992, Reistad and Giord 1994, Hughes and Pareto 1999). It extends previous approaches by using abstract interpretation techniques to automatically infer linear approximations of the sizes of recursive data types and the stack and heap costs of recursive functions. The correctness of the analysis is formally proved with respect to an operational semantics for the language and an inference algorithm that automatically reconstructs size and cost bounds is presented. A prototype implementation of the analysis and operational semantics has been constructed and used to experimentally assess the quality of the cost bounds with some examples, including implementations of textbook functional programming algorithms and simplified embedded systems. Sat, 01 Nov 2008 00:00:00 GMT http://hdl.handle.net/10023/564 2008-11-01T00:00:00Z Vasconcelos, Pedro B. Programming resource-sensitive systems, such as real-time embedded systems, requires guaranteeing both the functional correctness of computations and also that time and space usage fits within constraints imposed by hardware limits or the environment. Functional programming languages have proved very good at meeting the former logical kind of guarantees but not the latter resource guarantees. This thesis contributes to demonstrate the applicability of functional programming in resource-sensitive systems with an automatic program analysis for obtaining guaranteed upper bounds on dynamic space usage of functional programs. Our analysis is developed for a core subset of Hume, a domain-specific functional language targeting resource-sensitive systems (Hammond et al. 2007), and presented as a type and effect system that builds on previous sized type systems (Hughes et al. 1996, Chin and Khoo 2001) and effect systems for costs (Dornic et al. 1992, Reistad and Giord 1994, Hughes and Pareto 1999). It extends previous approaches by using abstract interpretation techniques to automatically infer linear approximations of the sizes of recursive data types and the stack and heap costs of recursive functions. The correctness of the analysis is formally proved with respect to an operational semantics for the language and an inference algorithm that automatically reconstructs size and cost bounds is presented. A prototype implementation of the analysis and operational semantics has been constructed and used to experimentally assess the quality of the cost bounds with some examples, including implementations of textbook functional programming algorithms and simplified embedded systems. http://hdl.handle.net/10023/522 Abstract: Learning to program is recognised nationally and internationally as a complex task that novices find challenging. There exist many endeavours to support the novice in this activity, including software tools that aim to provide a more supportive environment than that provided by standard software facilities, together with schemes that reduce the underlying complexity of programming by providing accessible micro-worlds in which students develop program code. Existing literature recognises that learning to program is difficult because of the need to learn the rules and operation of the language (program formulation), and the concurrent need to interpret problems and recognise the required components for that problem (problem formulation). This thesis describes a new form of learning support that addresses that dual task of program and problem formulation. A review of existing teaching tools that support the novice programmer leads to a set of requirements for a support tool that encompasses the processes of both program and problem formulation. This set of requirements is encapsulated in a conceptual framework for software tool development. The framework demonstrates how the requirements of a support tool can be met by performing a series of automated analyses at different stages in the student's development of a solution. An extended series of observations demonstrates the multi-faceted nature of problems that students encounter whilst they are learning to program and how these problems can be mapped onto the different levels of programs and problem formulation. These observations and the framework were used to inform the development of SNOOPIE, a sample instantiation of the framework for learning Java programming. This software tool has been fully evaluated and demonstrated to have a significant impact on the learning process for novice Java programmers. SNOOPIE is fully integrated into a current introductory programming module and a future programme of work is being established that will see SNOOPIE integrated with other established software tools. Wed, 25 Jun 2008 00:00:00 GMT http://hdl.handle.net/10023/522 2008-06-25T00:00:00Z Coull, Natalie J. Learning to program is recognised nationally and internationally as a complex task that novices find challenging. There exist many endeavours to support the novice in this activity, including software tools that aim to provide a more supportive environment than that provided by standard software facilities, together with schemes that reduce the underlying complexity of programming by providing accessible micro-worlds in which students develop program code. Existing literature recognises that learning to program is difficult because of the need to learn the rules and operation of the language (program formulation), and the concurrent need to interpret problems and recognise the required components for that problem (problem formulation). This thesis describes a new form of learning support that addresses that dual task of program and problem formulation. A review of existing teaching tools that support the novice programmer leads to a set of requirements for a support tool that encompasses the processes of both program and problem formulation. This set of requirements is encapsulated in a conceptual framework for software tool development. The framework demonstrates how the requirements of a support tool can be met by performing a series of automated analyses at different stages in the student's development of a solution. An extended series of observations demonstrates the multi-faceted nature of problems that students encounter whilst they are learning to program and how these problems can be mapped onto the different levels of programs and problem formulation. These observations and the framework were used to inform the development of SNOOPIE, a sample instantiation of the framework for learning Java programming. This software tool has been fully evaluated and demonstrated to have a significant impact on the learning process for novice Java programmers. SNOOPIE is fully integrated into a current introductory programming module and a future programme of work is being established that will see SNOOPIE integrated with other established software tools. http://hdl.handle.net/10023/435 Abstract: In this thesis we demonstrate the algorithmic usefulness of the so-called Mal'cev correspondence for computations with infinite polycyclic groups. This correspondence between Q-powered nilpotent groups and rational nilpotent Lie algebras was discovered by Anatoly Mal'cev in 1951. We show how the Mal'cev correspondence can be realized on a computer. We explore two possibilities for this purpose and compare them: the first one uses matrix embeddings and the second the Baker-Campbell-Hausdorff formula. Then, we describe a new collection algorithm for polycyclically presented groups, which we call Mal'cev collection. Algorithms for collection lie at the heart of most methods dealing with polycyclically presented groups. The current state of the art is "collection from the left" as recently studied by Gebhardt, Leedham-Green/Soicher and Vaughan-Lee. Mal'cev collection is in some cases dramatically faster than collection from the left, while using less memory. Further, we explore how the Mal'cev correspondence can be used to describe symbolically the collection process in polycyclically presented groups. In particular, we describe an algorithm that computes the collection functions for splittable polycyclic groups. This algorithm is based on work by du Sautoy. We apply it to the computation of pro-p-completions of polycyclic groups. Finally we describe a practical algorithm for testing polycyclicity of finitely generated rational matrix groups. Previously, not only did no such method exist but it was not clear whether this question was decidable at all. Most of the methods described in this thesis are implemented in the computer algebra system GAP and publicly available as part of the GAP packages Guarana and Polenta. Reports on the implementation including runtimes for some examples are given at the appropriate places. Fri, 30 Nov 2007 00:00:00 GMT http://hdl.handle.net/10023/435 2007-11-30T00:00:00Z Assmann, Björn In this thesis we demonstrate the algorithmic usefulness of the so-called Mal'cev correspondence for computations with infinite polycyclic groups. This correspondence between Q-powered nilpotent groups and rational nilpotent Lie algebras was discovered by Anatoly Mal'cev in 1951. We show how the Mal'cev correspondence can be realized on a computer. We explore two possibilities for this purpose and compare them: the first one uses matrix embeddings and the second the Baker-Campbell-Hausdorff formula. Then, we describe a new collection algorithm for polycyclically presented groups, which we call Mal'cev collection. Algorithms for collection lie at the heart of most methods dealing with polycyclically presented groups. The current state of the art is "collection from the left" as recently studied by Gebhardt, Leedham-Green/Soicher and Vaughan-Lee. Mal'cev collection is in some cases dramatically faster than collection from the left, while using less memory. Further, we explore how the Mal'cev correspondence can be used to describe symbolically the collection process in polycyclically presented groups. In particular, we describe an algorithm that computes the collection functions for splittable polycyclic groups. This algorithm is based on work by du Sautoy. We apply it to the computation of pro-p-completions of polycyclic groups. Finally we describe a practical algorithm for testing polycyclicity of finitely generated rational matrix groups. Previously, not only did no such method exist but it was not clear whether this question was decidable at all. Most of the methods described in this thesis are implemented in the computer algebra system GAP and publicly available as part of the GAP packages Guarana and Polenta. Reports on the implementation including runtimes for some examples are given at the appropriate places. http://hdl.handle.net/10023/319 Abstract: At the heart of the connections between Proof Theory and Type Theory, the Curry-Howard correspondence provides proof-terms with computational features and equational theories, i.e. notions of normalisation and equivalence. This dissertation contributes to extend its framework in the directions of proof-theoretic formalisms (such as sequent calculus) that are appealing for logical purposes like proof-search, powerful systems beyond propositional logic such as type theories, and classical (rather than intuitionistic) reasoning. Part I is entitled Proof-terms for Intuitionistic Implicational Logic. Its contributions use rewriting techniques on proof-terms for natural deduction (Lambda-calculus) and sequent calculus, and investigate normalisation and cut-elimination, with call-by-name and call-by-value semantics. In particular, it introduces proof-term calculi for multiplicative natural deduction and for the depth-bounded sequent calculus G4. The former gives rise to the calculus Lambdalxr with explicit substitutions, weakenings and contractions that refines the Lambda-calculus and Beta-reduction, and preserves strong normalisation with a full notion of composition of substitutions. The latter gives a new insight to cut-elimination in G4. Part II, entitled Type Theory in Sequent Calculus develops a theory of Pure Type Sequent Calculi (PTSC), which are sequent calculi that are equivalent (with respect to provability and normalisation) to Pure Type Systems but better suited for proof-search, in connection with proof-assistant tactics and proof-term enumeration algorithms. Part III, entitled Towards Classical Logic, presents some approaches to classical type theory. In particular it develops a sequent calculus for a classical version of System F_omega. Beyond such a type theory, the notion of equivalence of classical proofs becomes crucial and, with such a notion based on parallel rewriting in the Calculus of Structures, we compute canonical representatives of equivalent proofs. Fri, 08 Dec 2006 00:00:00 GMT http://hdl.handle.net/10023/319 2006-12-08T00:00:00Z Lengrand, Stéphane J. E. At the heart of the connections between Proof Theory and Type Theory, the Curry-Howard correspondence provides proof-terms with computational features and equational theories, i.e. notions of normalisation and equivalence. This dissertation contributes to extend its framework in the directions of proof-theoretic formalisms (such as sequent calculus) that are appealing for logical purposes like proof-search, powerful systems beyond propositional logic such as type theories, and classical (rather than intuitionistic) reasoning. Part I is entitled Proof-terms for Intuitionistic Implicational Logic. Its contributions use rewriting techniques on proof-terms for natural deduction (Lambda-calculus) and sequent calculus, and investigate normalisation and cut-elimination, with call-by-name and call-by-value semantics. In particular, it introduces proof-term calculi for multiplicative natural deduction and for the depth-bounded sequent calculus G4. The former gives rise to the calculus Lambdalxr with explicit substitutions, weakenings and contractions that refines the Lambda-calculus and Beta-reduction, and preserves strong normalisation with a full notion of composition of substitutions. The latter gives a new insight to cut-elimination in G4. Part II, entitled Type Theory in Sequent Calculus develops a theory of Pure Type Sequent Calculi (PTSC), which are sequent calculi that are equivalent (with respect to provability and normalisation) to Pure Type Systems but better suited for proof-search, in connection with proof-assistant tactics and proof-term enumeration algorithms. Part III, entitled Towards Classical Logic, presents some approaches to classical type theory. In particular it develops a sequent calculus for a classical version of System F_omega. Beyond such a type theory, the notion of equivalence of classical proofs becomes crucial and, with such a notion based on parallel rewriting in the Calculus of Structures, we compute canonical representatives of equivalent proofs. http://hdl.handle.net/10023/223 Abstract: This thesis describes the design of a novel class of pollsterless voting schemes. Many cryptographic voting schemes necessitate a pollster because the client side computations are beyond the understanding or ability of the voter. Such interactions require that the voter trust the software to perform operations on their behalf, and in effect, the pollster acts as the voter. Conversely, the pollsterless schemes presented here permit voters to interact with an election authority directly, without complex computations. Pollsterless schemes have the additional advantage of permitting voting on virtually any networked device, increasing the potential mobility of voting. The proposed pollsterless schemes are implemented and then evaluated with respect to the particular requirements of the UK public election context. The flexibility of pollsterless schemes in particular are demonstrated to fulfill the diverse requirements that may arise in this context, whilst the mobility of pollsterless schemes is demonstrated to fulfill requirements to improve the convenience of voting. Tue, 19 Jun 2007 00:00:00 GMT http://hdl.handle.net/10023/223 2007-06-19T00:00:00Z Storer, Timothy W. This thesis describes the design of a novel class of pollsterless voting schemes. Many cryptographic voting schemes necessitate a pollster because the client side computations are beyond the understanding or ability of the voter. Such interactions require that the voter trust the software to perform operations on their behalf, and in effect, the pollster acts as the voter. Conversely, the pollsterless schemes presented here permit voters to interact with an election authority directly, without complex computations. Pollsterless schemes have the additional advantage of permitting voting on virtually any networked device, increasing the potential mobility of voting. The proposed pollsterless schemes are implemented and then evaluated with respect to the particular requirements of the UK public election context. The flexibility of pollsterless schemes in particular are demonstrated to fulfill the diverse requirements that may arise in this context, whilst the mobility of pollsterless schemes is demonstrated to fulfill requirements to improve the convenience of voting. http://hdl.handle.net/10023/154 Abstract: Middleware augments operating systems and network infrastructure to assist in the creation of distributed applications in a heterogeneous environment. Current middleware systems exhibit some or all of the following five main problems: 1. Decisions must be made early in the design process. 2. Applications are inflexible to dynamic changes in their distribution. 3. Application development is complex and error-prone. 4. Existing systems force an unnatural encoding of application-level semantics. 5. Approaches to the specification of distribution policy are limited. This thesis defines a taxonomy of existing middleware systems and describes their limitations. The requirements that must be met by a third generation middleware system are defined and implemented by a system called the RAFDA Run-Time (RRT). The RRT allows control over the extent to which inter-address-space communication is exposed to programmers, aiding the creation, maintenance and evolution of distributed applications. The RRT permits the introduction of distribution into applications quickly and with minimal programmer effort, allowing for quick application prototyping. Programmers can conceal or expose the distributed nature of applications as required. The RRT allows instances of arbitrary application classes to be exposed to remote access as Web Services, provides control over the parameter-passing semantics applied to remote method calls and permits the creation of flexible distribution policies. The design of the RRT is described and evaluated qualitatively in the context of a case study based around the implementation of a peer-to-peer overlay network. A prototype implementation of the RRT is examined and evaluated quantitatively. Programmers determine the trade off between flexibility and simplicity offered by the RRT on a per-application basis, by concealing or exposing inter-address-space communication. The RRT is a middleware system that adapts to the needs of applications, rather than forcing distributed applications to adapt to the needs of the middleware system. Sun, 01 Jan 2006 00:00:00 GMT http://hdl.handle.net/10023/154 2006-01-01T00:00:00Z Walker, Scott Mervyn Middleware augments operating systems and network infrastructure to assist in the creation of distributed applications in a heterogeneous environment. Current middleware systems exhibit some or all of the following five main problems: 1. Decisions must be made early in the design process. 2. Applications are inflexible to dynamic changes in their distribution. 3. Application development is complex and error-prone. 4. Existing systems force an unnatural encoding of application-level semantics. 5. Approaches to the specification of distribution policy are limited. This thesis defines a taxonomy of existing middleware systems and describes their limitations. The requirements that must be met by a third generation middleware system are defined and implemented by a system called the RAFDA Run-Time (RRT). The RRT allows control over the extent to which inter-address-space communication is exposed to programmers, aiding the creation, maintenance and evolution of distributed applications. The RRT permits the introduction of distribution into applications quickly and with minimal programmer effort, allowing for quick application prototyping. Programmers can conceal or expose the distributed nature of applications as required. The RRT allows instances of arbitrary application classes to be exposed to remote access as Web Services, provides control over the parameter-passing semantics applied to remote method calls and permits the creation of flexible distribution policies. The design of the RRT is described and evaluated qualitatively in the context of a case study based around the implementation of a peer-to-peer overlay network. A prototype implementation of the RRT is examined and evaluated quantitatively. Programmers determine the trade off between flexibility and simplicity offered by the RRT on a per-application basis, by concealing or exposing inter-address-space communication. The RRT is a middleware system that adapts to the needs of applications, rather than forcing distributed applications to adapt to the needs of the middleware system.