Abstract
We study the problem of querying data sources that accept only a limited set of queries, such as sources accessible by Web services which can implement very large (potentially infinite) families of queries. We revisit a classical setting in which the application queries are conjunctive queries and the source accepts families of conjunctive queries specified as the expansions of a (potentially recursive) Datalog program with parameters.We say that query Q is expressible by the program \(\ensuremath{\mathcal{P}}\) if it is equivalent to some expansion of \(\ensuremath{\mathcal{P}}\). Q is supported by \(\ensuremath{\mathcal{P}}\) if it has an equivalent rewriting using some finite set of \(\ensuremath{\mathcal{P}}\)’s expansions. We present the first study of expressibility and support for sources that satisfy integrity constraints, which is generally the case in practice.
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