Showing papers by "Hector J. Levesque published in 1982"

Competence in knowledge representation

Abstract: The range of domains and tasks for “knowledgebased systems” has been expanding at a furious pace. As we move away from trivial domains, such as the “blocks world”, the demands on knowledge representation systems used by expert programs are becoming more extreme. For one thing, the domains themselves are getting so complex that specialized technical vocabularies are unavoidable; consequently, the issue of a system talking with un expert in ki8 own ianguage cannot be ignored. For another, tasks such as medical diagnosis, scene analysis, speech understanding, and game playing all have as a central feature an incrementally evolving model representing probably incomplete knowledge of part of the task domain. In this paper, we explore some of the impact of these two critical issues-complexity and incompletenesson knowledge representation systems. We review some aspects of current representation research that offer a foundation for coping with these problems, and finally suggest a way of integrating these ideas into a powerful, practical knowledge representation paradigm.

A formal treatment of incomplete knowledge bases

Abstract: The formal representation issues underlying the use of incomplete knowledge bases are investigated. It is argued that to effectively deal with incomplete knowledge, a system must first be able to determine where the incompleteness lies. This has two consequences: first, the knowledge base must have knowledge about its own incompleteness and second, it must be possible to ask or tell the knowledge base about its incompleteness. A formal model of knowledge bases with these abilities is presented. The characterization is in terms of a logical language that can refer both to application domains and to what knowledge bases might know about such domains. This language is also used to formulate questions, statements and defaults for a knowledge base. A semantic and proof-theoretic analysis is provided not only for the language itself, but also for the operations of answering questions, acquiring knowledge and assuming defaults.