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We study a general framework for query rewriting in the presence of an arbitrary first-order logic ontology over a database signature. The framework supports deciding the existence of a safe-range first-order equivalent reformulation of a query in terms of the database signature, and if so, it provides an effective approach to construct the reformulation(More)
We investigate the computational cost of combining the open and closed world assumptions in Description Logics. Unlike previous works, which have considered data complexity and focused mostly on lightweight DLs, we study combined complexity for a wide range of DLs, from lightweight to very expressive ones. From existing results for the standard setting,(More)
We study a general framework for query rewriting in the presence of an arbitrary first-order logic ontology over a database signature. The framework supports deciding the existence of a safe-range first-order equivalent reformulation of a query in terms of the database signature, and if so, it provides an effective approach to construct the reformulation(More)
Query answering over databases with conceptual constraints is an important problem in database theory. To deal with the problem, the ontology-based data access approach uses ontologies to capture both constraints and databases. In this approach, databases are considered under open-world assumption which creates many issues including the necessity of(More)