Query Rewriting Using Datalog for Duplicate Resolution

Abstract

Matching Dependencies (MDs) are a recent proposal for declarative entity resolution. They are rules that specify, given the similarities satisfied by values in a database, what values should be considered duplicates, and have to be matched. On the basis of a chase-like procedure for MD enforcement, we can obtain clean (duplicate-free) instances; actually possibly several of them. The clean answers to queries (which we call the resolved answers) are invariant under the resulting class of instances. In this paper, we investigate a query rewriting approach to obtaining the resolved answers (for certain classes of queries and MDs). The rewritten queries are specified in stratified Datalog not,s with aggregation. In addition to the rewriting algorithm, we discuss the semantics of the rewritten queries, and how they could be implemented by means of a DBMS.

Tractable vs. Intractable Cases of Query Answering under Matching Dependencies

“…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].…”

“…We call them changeable attribute queries. [13,14] cases of cyclic sets of MDs, we complement these results by studying the complexity of RQA for sets of MDs that do not have cycles.…”

“…In [13,14], a query rewriting methodology for computing resolved answers to queries under MDs was presented. In this case, the rewritten queries turn out to be Datalog queries with counting, and can be obtained for two main kinds of sets of MDs: (a) MDs do not depend on each other, i.e.…”

“…However, for the chase sequences that do terminate in a minimally resolved instance, the chase imposes a relatively easily characterizable structure [14,13], allowing us to obtain a query rewriting methodology. So, cycles help us achieve tractability for some classes of queries [13] (cf. Section 2.2).…”

Tractable vs. Intractable Cases of Matching Dependencies for Query Answering under Entity Resolution

“…The resolved query answering problem was studied further in [18,17]. Specifically, a class of tractable cases of the problem was identified [18], for which a method for retrieving the resolved answers based on query rewriting into stratified Datalog with aggregation was developed [17].…”