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A Possible World Semantics for Disjunctive Databases
April 1993 (vol. 5 no. 2)
pp. 282-292

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.

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Index Terms:
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
Citation:
E.P.F. Chan, "A Possible World Semantics for Disjunctive Databases," IEEE Transactions on Knowledge and Data Engineering, vol. 5, no. 2, pp. 282-292, April 1993, doi:10.1109/69.219736
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