In the Semantic Web, the goal is offering access to information that is distributed over the Internet. Data integration is highly relevant in this context, since it consists in providing a uniform access to a set of data sources, through a unified representation of the data called global schema. Integrity constraints (ICs) are expressed on the global schema in order to better represent the domain of interest, yet such constraints may not be satisfied by the data at the sources. In this paper we address the problem of answering queries posed to a data integration system where the mapping is specified in the so-called GLAV approach, and when tuple-generating dependencies (TGDs) and functional dependencies (FDs) are expressed over the global schema. We extend previous results by first showing that, in the case of TGDs without FDs, known query rewriting techniques can be applied in a more general case, and can take into account also the GLAV mapping in a single rewriting step. Then we introduce FDs with TGDs, identifying a novel class of ICs for which query answering is decidable, and providing a query answering algorithm based on query rewriting also in this case.
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