An extension to GCWA and query evaluation for disjunctive deductive databases

We present a simple and intuitive extension GCWA(G) of the generalized clos ed world assumption (GCWA) from positive disjunctive deductive databases to general disjunctive deductive databases (with default negation). This sema ntics is defined in terms of unfounded sets and possesses an argumentation- theoretic characterization. We also provide a top-down procedure for GCWA(G ), which is sound and complete with respect to GCWA(G). We investigate two query evaluation methods for GCWA(G): database partition, and database spli tting. The basic idea of these methods is to divide the original deductive database into several smaller sub-databases and the query evaluation in the original database is transformed into the problem of query evaluation in s maller or simplified components. We prove that these two methods of query e valuation are all sound with respect to GCWA(G).