A formal treatment of incomplete knowledge bases
Hector J. Levesque · 1982
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.