We study the expressiveness and the complexity of static analysis of extended conjunctive regular path queries (ECRPQs), introduced by Barceló et al. (PODS '10). ECRPQs are an extension of con- junctive regular path queries (CRPQs), a well-studied language for querying graph structured databases. Our first main result shows that query containment and equivalence of a CRPQ in an ECRPQ is undecidable. This settles one of the main open problems posed by Barceló et al. As a second main result, we prove a non-recursive succinctness gap between CRPQs and the CRPQ-expressible fragment of ECRPQs. Apart from this, we develop a tool for proving inexpressibility results for CRPQs and ECRPQs. In particular, this enables us to show that there exist queries definable by regular expressions with backreferencing, but not expressible by ECRPQs.
Published inCEUR Workshop Proceedings
CitationFREYDENBERGER, D.D. and SCHWEIKARDT, N., 2011. Expressiveness and static analysis of extended conjunctive regular path queries. IN: Barceló, P. and Tannen, V. (eds). CEUR Workshop Proceedings: Proceedings of the 5th Alberto Mendelzon International Workshop on Foundations of Data Management (AMW2011), Santiago, Chile, May 9-12, 2011, vol. 749, paper 9
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Book seriesCEUR Workshop Proceedings;749