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- Alin Deutsch, Alan Nash, Jeffrey B. Remmel
- PODS
- 2008

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)

- Alan Nash, Luc Segoufin, Victor Vianu
- ACM Trans. Database Syst.
- 2005

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)

- Alin Deutsch, Bertram Ludäscher, Alan Nash
- ICDT
- 2005

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)

- Georg Gottlob, Alan Nash
- J. ACM
- 2008

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)

- Georg Gottlob, Alan Nash
- PODS
- 2006

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)

- Ronald Fagin, Phokion G. Kolaitis, Alan Nash, Lucian Popa
- PODS
- 2008

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)

- Alan Nash, Luc Segoufin, Victor Vianu
- ICDT
- 2007

- Ronald Fagin, Alan Nash
- J. ACM
- 2010

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)

- Alan Nash, Philip A. Bernstein, Sergey Melnik
- ACM Trans. Database Syst.
- 2005

Composition of mappings between schemas is essential to support schema evolution, data exchange, data integration, and other data management tasks. In many applications, mappings are given by embedded dependencies. In this paper, we study the issues involved in composing such mappings.

- Philip A. Bernstein, Todd J. Green, Sergey Melnik, Alan Nash
- VLDB
- 2006

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)