Containment of UC2RPQ: the hard and easy cases
Résumé
We study the containment problem for UC2RPQ, that is, two-way Regular Path Queries, closed under conjunction, projection and union. We show a dichotomy property between PSpace-c and ExpSpace-c in terms of the shape of queries, based on a property on its underlying graph. We show that for any class C of graphs, the containment problem for queries whose underlying graph is in C is in PSpace if and only if C has bounded bridgewidth. Bridgewidth is a graph measure we introduce, defined as the maximum size of a minimal edge separator of a graph.
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