Virtual views are a mechanism that facilitates re-use and makes queries easier to express. However the use of iterative view definitions makes very simple query evaluation and analysis problems more complex. In this paper we study classical containment and equivalence problems for queries built up through simple unions of conjunctive queries and view definitions. More precisely, we determine the complexity of containment and equivalence for non-recursive Datalog. We show that the problem is much harder than its classical counterpart – complete for co-NEXPTIME. We then show that this remains true even with restrictions on the schema and queries in place. Finally, we isolate subcases that are more tractable, ranging from NP to PSPACE
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