Querying Conceptual Schemata with Expressive Equality Constraints
When querying data through a conceptual schema or ontology, we compute answers entailed by the logical theory constituted by the data plus the conceptual schema. Traditional database constraints like tuple-generating dependencies (TGDs) and equality-generating dependencies (EGDs) are a useful tool for ontology specification. However, their interaction leads to undecidability of query answering even in simple cases. In this paper we exhibit a novel and general class of EGDs that, together with a relevant class of TGDs, ensures decidability of query answering. Our results capture well-known ontology languages as special cases; in particular, they allow us to deal with extended Entity-Relationship schemata enriched with expressive equality constraints.
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