Access patterns and integrity constraints revisited

We consider which queries are answerable in the presence of access restrictions and integrity constraints, and which portions of the schema are accessible in the presence of access restrictions and constraints. Unlike prior work, we focus on integrity constraint languages that subsume inclusion dependencies. We also use a semantic definition of answerability: a query is answerable if the accessible information is sufficient to determine its truth value. We show that answerability is decidable for the class of guarded dependencies, which includes all inclusion dependencies, and also for constraints given in the guarded fragment of first-order logic. We also show that answerable queries have "query plans" in a restricted language. We give corresponding results for extractability of portions of the schema. Our results relate querying with limited access patterns, determinacy-vsrewriting, and analysis of guarded constraints.