Learn More
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 finding minimal containing and maximal contained rewritings and for deciding whether an exact rewriting exists. We show that rewriting queries using views in this case(More)
Data exchange deals with inserting data from one database into another database having a different schema. Fagin et al. &lsqb;2005&rsqb; have shown that among the universal solutions of a solvable data exchange problem, there exists&#8212;up to isomorphism&#8212;a unique most compact one, &#8220;the core&#8221;, and have convincingly argued that this core(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)
We study the problem of answering queries over sources with limited access patterns. The problem is to decide whether a given query Q is feasible, i.e., equivalent to an executable query Q that observes the limited access patterns given by the sources. We characterize the complexity of deciding feasibility for the classes CQ ¬ (conjunctive queries with(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)