Classification of annotation semirings over containment of conjunctive queries
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We study the problem of query containment of conjunctive queries over annotated databases. Annotations are typically attached to tuples and represent metadata, such as probability, multiplicity, comments, or provenance. It is usually assumed that annotations are drawn from a commutative semiring. Such databases pose new challenges in query optimization, since many related fundamental tasks, such as query containment, have to be reconsidered in the presence of propagation of annotations. We axiomatize several classes of semirings for each of which containment of conjunctive queries is equivalent to existence of a particular type of homomorphism. For each of these types, we also specify all semirings for which existence of a corresponding homomorphism is a sufficient (or necessary) condition for the containment. We develop new decision procedures for containment for some semirings which are not in any of these classes. This generalizes and systematizes previous approaches.
Kostylev , E V , Reutter , J L & Salamon , A Z 2014 , ' Classification of annotation semirings over containment of conjunctive queries ' , ACM Transactions on Database Systems , vol. 39 , no. 1 , 1 , pp. 1-39 . https://doi.org/10.1145/2556524
ACM Transactions on Database Systems
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DescriptionFunding: This work is supported under SOCIAM: The Theory and Practice of Social Machines, a project funded by the UK Engineering and Physical Sciences Research Council (EPSRC) under grant number EP/J017728/1. This work was also supported by FET-Open Project FoX, grant agreement 233599; EPSRC grants EP/F028288/1, G049165 and J015377; and the Laboratory for Foundations of Computer Science.
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