Issue No. 02 - April (1993 vol. 5)
DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/69.219736
<p>The fundamental problem that arises when a ground atom in a disjunctive database is assumed false is discussed. There are basically two different approaches for inferring negative information for disjunctive databases: J. Minker's (1982) generalized closed world assumption (GCWA) and K.A. Ross and R.W. Topor's (1988) disjunctive database rule (DDR). It is argued that neither approach is satisfactory. A database semantics called PWS is proposed. It is shown that for propositional databases with no negative clauses, the problem of determining if a negative ground literal is inferred under the GCWA is co-NP-hard, while the same problem can be solved efficiently under the DDR and PWS. However, in the general case, the problem becomes co-NP-complete for the DDR and PWS. Relationships among GCWA, DDR, and PWS are highlighted. In general, disjunctive clauses are interpreted inclusively under the DDR and unpredictably under the GCWA.</p>
possible world semantics; ground atom; disjunctive database; negative information; generalized closed world assumption; GCWA; disjunctive database rule; DDR; database semantics; PWS; propositional databases; negative ground literal; co-NP-hard; database theory; deductive databases; knowledge based systems
E. Chan, "A Possible World Semantics for Disjunctive Databases," in IEEE Transactions on Knowledge & Data Engineering, vol. 5, no. , pp. 282-292, 1993.