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We revisit the standard chase procedure, studying its properties and applicability to classical database problems. We settle (in the negative) the open problem of decidability of termination of the standard chase, and we provide sufficient termination conditions which are strictly less over-conservative than the best previously known. We investigate the… (More)

We investigate the question of whether a query <i>Q</i> can be answered using a set V of views. We first define the problem in information-theoretic terms: we say that V determines <i>Q</i> if V provides enough information to uniquely determine the answer to <i>Q.</i> Next, we look at the problem of rewriting <i>Q</i> in terms of V using a specific… (More)

We study the problem of rewriting queries using views in the presence of access patterns, integrity constraints, disjunction and negation. We provide asymptotically optimal algorithms for (1) finding minimally containing and (2) maximally contained rewritings respecting the access patterns (which we call executable) and for (3) deciding whether an exact… (More)

Data exchange deals with inserting data from one database into another database having a different schema. We study and solve a central computational problem of data exchange, namely, computing the core of a universal solution to a data exchange problem. Fagin, Kolaitis, and Popa [9], have shown that among the universal solutions of a solvable data exchange… (More)

Data exchange deals with inserting data from one database into another database having a different schema. Fagin et al. [2005] have shown that among the universal solutions of a solvable data exchange problem, there exists—up to isomorphism—a unique most compact one, “the core”, and have convincingly argued that this core… (More)

The existence of a language expressing precisely the PTIME queries on arbitrary structures remains the central open problem in the theory of database query languages. As it turns out, two variants of this question have been formulated. Surprisingly, despite the importance of the problem, the relationship between these variants has not been systematically… (More)

Mapping composition is a fundamental operation in metadata driven applications. Given a mapping over schemas σ<inf>1</inf> and σ<inf>2</inf> and a mapping over schemas σ<inf>2</inf> and σ<inf>3</inf>, the composition problem is to compute an equivalent mapping over σ<inf>1</inf> and σ<inf>3</inf>. We describe a new composition… (More)

A schema mapping is a high-level specification that describes the relationship between two database schemas. As schema mappings constitute the essential building blocks of data exchange and data integration, an extensive investigation of the foundations of schema mappings has been carried out in recent years. Even though several different aspects of schema… (More)

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). The notion of an inverse of a schema mapping is subtle, because a schema mapping may associate many target instances with each source instance, and many source… (More)