3,887 research outputs found

    Automatic generation of simplified weakest preconditions for integrity constraint verification

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    Given a constraint cc assumed to hold on a database BB and an update uu to be performed on BB, we address the following question: will cc still hold after uu is performed? When BB is a relational database, we define a confluent terminating rewriting system which, starting from cc and uu, automatically derives a simplified weakest precondition wp(c,u)wp(c,u) such that, whenever BB satisfies wp(c,u)wp(c,u), then the updated database u(B)u(B) will satisfy cc, and moreover wp(c,u)wp(c,u) is simplified in the sense that its computation depends only upon the instances of cc that may be modified by the update. We then extend the definition of a simplified wp(c,u)wp(c,u) to the case of deductive databases; we prove it using fixpoint induction

    The Constructive method for query containment checking (extended version)

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    We present a new method that checks Query Containment for queries with negated derived atoms and/or integrity constraints. Existing methods for Query Containment checking that deal with these cases do not check actually containment but another related property called uniform containment, which is a sufficient but not necessary condition for containment. Our method can be seen as an extension of the canonical databases approach beyond the class of conjunctive queries.Postprint (published version

    A Rational and Efficient Algorithm for View Revision in Databases

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    The dynamics of belief and knowledge is one of the major components of any autonomous system that should be able to incorporate new pieces of information. In this paper, we argue that to apply rationality result of belief dynamics theory to various practical problems, it should be generalized in two respects: first of all, it should allow a certain part of belief to be declared as immutable; and second, the belief state need not be deductively closed. Such a generalization of belief dynamics, referred to as base dynamics, is presented, along with the concept of a generalized revision algorithm for Horn knowledge bases. We show that Horn knowledge base dynamics has interesting connection with kernel change and abduction. Finally, we also show that both variants are rational in the sense that they satisfy certain rationality postulates stemming from philosophical works on belief dynamics

    Open issues in semantic query optimization in relational DBMS

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    After two decades of research into Semantic Query Optimization (SQO) there is clear agreement as to the efficacy of SQO. However, although there are some experimental implementations there are still no commercial implementations. We first present a thorough analysis of research into SQO. We identify three problems which inhibit the effective use of SQO in Relational Database Management Systems(RDBMS). We then propose solutions to these problems and describe first steps towards the implementation of an effective semantic query optimizer for relational databases
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