Phokion G. Kolaitis

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A schema mapping is a specification that describes how data structured under one schema (the source schema) is to be transformed into data structured under a different schema (the target schema). Schema mappings play a key role in numerous areas of database systems, including database design, information integration, and model management. A fundamental(More)
Data exchange is the problem of taking data structured under a source schema and creating an instance of a target schema that reflects the source data as accurately as possible. Given a source instance, there may be many solutions to the data exchange problem, that is, many target instances that satisfy the constraints of the data exchange problem. In an(More)
We identify the computational complexity of the satisfiability problem for FO, the fragment of first-order logic consisting of all relational first-order sentences with at most two distinct variables. Although this fragment was shown to be decidable a long time ago, the computational complexity of its decision problem has not been pinpointed so far. In 1975(More)
Conjunctive query containment is recognized as a fundamental problem in database query evaluation and optimization At the same time constraint satisfaction is recog nized as a fundamental problem in arti cial intelligence What do conjunctive query containment and constraint satisfaction have in common Our main conceptual con tribution in this paper is to(More)
Boolean satisfiability problems are an important benchmark for questions about complexity, algorithms, heuristics and threshold phenomena. Recent work on heuristics, and the satisfiability threshold has centered around the structure and connectivity of the solution space. Motivated by this work, we study structural and connectivity-related properties of the(More)
We study here the language Datalog(&#8800;), which is the query language obtained from Datalog by allowing equalities and inequalities in the bodies of the rules. We view Datalog(&#8800;) as a fragment of an infinitary logic <italic>L</italic><supscrpt>&#969;</supscrpt> and show that <italic>L</italic><supscrpt>&#969;</supscrpt> can be characterized in(More)
We systematically investigate the connections between constraint satisfaction problems, structures of bounded treewidth, and definability in logics with a finite number of variables. We first show that constraint satisfaction problems on inputs of treewidth less than k are definable using Datalog programs with at most k variables; this provides a new(More)
Schema mappings are high-level specifications that describe the relationship between two database schemas. Two operators on schema mappings, namely the composition operator and the inverse operator, are regarded as especially important. Progress on the study of the inverse operator was not made until very recently, as even finding the exact semantics of(More)
Managing inconsistency in databases has long been recognized as an important problem. One of the most promising approaches to coping with inconsistency in databases is the framework of database repairs, which has been the topic of an extensive investigation over the past several years. Intuitively, a repair of an inconsistent database is a consistent(More)