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Classification of annotation semirings over containment of conjunctive queries

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http://dl.acm.org/citation.cfm?id=2556524
Original languageEnglish
Article number1
Number of pages39
JournalACM Transactions on Database Systems
Volume39
Issue number1
DOIs
Publication statusPublished - 6 Jan 2014

Abstract

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.

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