Querying Data Sources that Export Infinite Sets of Views

摘要

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 V if it is equivalent to some expansion of V. Q is supported by V if it has an equivalent rewriting using some finite set of Vs expansions. We present the first study of expressibility and support for sources that satisfy integrity constraints, which is generally the case in practice.