Persistent object stores

Abstract

The design and development of a type secure persistent object store is presented as part of an architecture to support experiments in concurrency, transactions and distribution. The persistence abstraction hides the physical properties of data from the programs that manipulate it. Consequently, a persistent object store is required to be of unbounded size, infinitely fast and totally reliable. A range of architectural mechanisms that can be used to simulate these three features is presented. Based on a suitable selection of these mechanisms, two persistent object stores are presented. The first store is designed for use with the programming language PS-algol. Its design is evolved to yield a more flexible layered architecture. The layered architecture is designed to provide each distinct architectural mechanism as a separate architectural layer conforming to a specified interface. The motivation for this design is two-fold. Firstly, the particular choice of layers greatly simplifies the resulting implementation and secondly, the layered design can support experimental architecture implementations. Since each layer conforms to a specified interface, it is possible to experiment with the implementation of an individual layer without affecting the implementation of the remaining architectural layers. Thus, the layered architecture is a convenient vehicle for experimenting with the implementation of persistent object stores. An implementation of the layered architecture is presented together with an example of how it may be used to support a distributed system. Finally, the architecture's ability to support a variety of storage configurations is presented.