A knowledge base may contain indefinite knowledge which can be represented by the set of Horn and non_Horn clauses. If a knowledge base contains non_Horn clauses, it cannot be represented directly by Prolog. In this thesis, the Modified Closed World Assumption(MCWA) is suggested to deal with indefinite knowledge in PROlog Knowledge Base called PROKB.
The query answering for PROKB is extended to handle indefinite answers. For this purpose, queries are divided into several types and the answering methods according to each type are presented.
When knowledge is added to a knowledge base containing non_Horn clauses, the knowledge base must always be consistent. The procedures to solve this problem are proposed.
