Foundations of Query Answering in Relational Data Exchange

Book excerpt: Relational data exchange is the problem of translating relational data according to a given specification. It is one of the many tasks that arise in information integration. A fundamental issue is how to answer queries that are posed against the result of the data exchange so that the answers are semantically consistent with the source data. For monotonic queries, the certain answers semantics by Fagin, Kolaitis, Miller, and Popa (2003) yields good answers. For many non-monotonic queries, however, this semantics was shown to yield counter-intuitive answers. This dissertation deals with the problem of computing the certain answers to monotonic queries on the one hand. On the other hand, it presents and compares semantics for answering non-monotonic queries, and investigates how hard it is to evaluate non-monotonic queries under these semantics.