Complexity of Query Answering in LogicDatabases with Complex
نویسنده
چکیده
This paper characterizes the computational complexity of nonrecursive queries in logic databases with complex values. Queries are represented by Horn clause logic programs. Complex values are represented by terms in equational theories ( nite sets and multisets are examples of such complex values). We show that the problem of whether a query has a nonempty answer is NEXP-hard for nonrecursive range-restricted queries. We also show that this problem is in NEXP if complex values satisfy the following condition: the solvability problem for equations in the corresponding equational theory is in NP. Since trees, nite sets and multisets satisfy this condition, the query answering problem for logic databases with trees, nite sets and multisets is shown to be NEXP-complete.2 2Copyright c 1997, 1998 Evgeni Dantsin and Andrei Voronkov. This technical report and other technical reports in this series can be obtained at http://www.csd.uu.se/papers/reports.html or at ftp.csd.uu.se in the directory pub/papers/reports. Some reports can be updated, check one of these addresses for the latest version. Evgeny Dantsin and Andrei Voronkov. Complexity of Query Answering in Logic Databases . . . 1
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