Database Repairing and Consistent Query Answering

Abstract

Synthesis Lectures on Data Management is edited by Tamer Özsu of the University of Waterloo. The series will publish 50-to 125-page publications on topics pertaining to data management. The scope will largely follow the purview of premier information and computer science conferences, such as ACM SIGMOD, VLDB, ICDE, PODS, ICDT, and ACM KDD. Potential topics include, but not are limited to: query languages, database system architectures, transaction management, data warehousing, XML and databases, data stream systems, wide scale data distribution, multimedia data management, data mining, and related subjects.

Tractable vs. Intractable Cases of Query Answering under Matching Dependencies

“…For certain pairs of MDs that satisfy a syntactic condition, we establish an intractability result, proving that deciding resolved answers to changeable attribute queries is NPhard in data. 4. For similarity relations that are transitive (a special case), we establish that the conditions for hardness mentioned in the previous item, lead to a dichotomy result: pairs of MDs that satisfy them are always hard, otherwise they are always easy (for RQA).…”

“…The definition of resolved answer reminds us of consistent query answering (CQA) [4], where much research has been about (polynomial-time) query rewriting methodologies. In all the cases identified in the literature (see [4,18] for recent surveys), the rewritings have been first-order.…”

“…In all the cases identified in the literature (see [4,18] for recent surveys), the rewritings have been first-order. For MDs, the exhibited rewritings are in Datalog [13].…”

Exchange-Repairs: Managing Inconsistency in Data Exchange

“…Detailed information about schema mappings and certain answers can be found in [3,19], and about repairs and consistent answers in [4,7].…”

“…Intuitively, the root cause for the lack of solutions is that the source instance contains inconsistent or conflicting information that is exposed by the target constraints of the schema mapping at hand. In turn, this suggests that alternative semantics for target queries could be obtained by adopting the notions of database repairs and consistent answers from the study of inconsistent databases (see [7] for an overview). We note that several different types of repairs have been studied in the context of inconsistent databases; the most widely used ones are the symmetric difference (⊕-repairs), which contain as special cases the subset-repairs and the superset-repairs.…”