Get Database Repairing and Consistent Query Answering PDF

By Leopoldo Bertossi, M. Tamer Ozsu

ISBN-10: 1608457621

ISBN-13: 9781608457625

Integrity constraints are semantic stipulations database should still fulfill to be able to be a suitable version of exterior truth. In perform, and for plenty of purposes, a database would possibly not fulfill these integrity constraints, and hence it's stated to be inconsistent. notwithstanding, and probably, a wide component of the database continues to be semantically right, in a feeling that should be made unique. After having supplied a proper characterization of constant facts in an inconsistent database, the typical challenge emerges of extracting that semantically right info, as question solutions. The constant information in an inconsistent database is generally characterised because the info that persists throughout all of the database cases which are constant and minimally range from the inconsistent example. these are the so-called upkeep of the database. specifically, the constant solutions to a question posed to the inconsistent database are these solutions that may be at the same time got from the entire database upkeep. As anticipated, the inspiration of fix calls for an sufficient proposal of distance that enables for the comparability of databases with recognize to how a lot they vary from the inconsistent example. in this foundation, the minimality on upkeep may be effectively formulated. during this monograph we current and talk about those basic strategies, diversified fix semantics, algorithms for computing constant solutions to queries, and in addition complexity-theoretic effects with regards to the computation of upkeep and doing constant question answering. desk of Contents: creation / The Notions of fix and constant resolution / Tractable CQA and question Rewriting / Logically Specifying maintenance / choice difficulties in CQA: Complexity and Algorithms / upkeep and knowledge cleansing

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When D is inconsistent wrt the FDs , it may hold that σ (D) has extra tuples wrt D, and does not satisfy either. Next, tuple-deletion-based repairs wrt are applied to σ (D), obtaining a class of repairs Repts(σ (D), ) for D. Depending on the choice of σ , attribute-based repairs for D wrt can be simulated via the repairs in Repts(σ (D), ). 13 D [Wijsen, 2006] Consider the following universal relation with a set Name An Ed Birth 1964 1962 Sex F M ZIP 7000 7000 of FDs: Name → {Birth, Sex, ZIP}, ZIP → City.

If we want to compute consistent information, in particular consistent answers to queries, we may try to avoid explicitly computing and materializing repairs. As the following example shows, there may be too many of them. , 2003b] The following instance is inconsistent wrt the FD R : A → B. 4 A 1 1 · n n There are n pairs of tuples that, in combination, violate the FD. , an exponential number in the size of the original instance. B 0 1 · 0 1 WHAT DO WE DO THEN? For the moment, and loosely speaking, (the problem of ) consistent query answering (CQA) will refer to the problem of deciding if a tuple is a consistent answer to a query or to the problem of computing all the consistent answers to a query.

This repair semantics is applied when the database at hand is considered to be incomplete and is then completed via additional tuple insertions. 6 we have: D2 ∈ Repis(D, IC), / Repis(D, IC). but D1 ∈ 2 If we wanted the partial order to capture the fact that only tuple deletions are allowed, we could add the extra condition that (D1 D) = (D2 the partial order. D) = ∅. However, it is easier to specify first the kind of operations allowed, and then, on that basis, define 18 2. THE NOTIONS OF REPAIR AND CONSISTENT ANSWER As indicated above, an important issue is that, when the inclusion dependencies have existential quantifiers, then values have to be invented for them.

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Database Repairing and Consistent Query Answering by Leopoldo Bertossi, M. Tamer Ozsu


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