Abstract: This paper explored knowledge update based on description logic Al C(}'.First, it introduced the syntax and semantics of ALCO@，secondly it proposed the concept of determined set and conflict set, after that it gave the algorithm which can obtain determined set and conflict set from the original knowledge set according to the Tableau algorithm of description logic. In the algorithm of update, we deleted assertions of Conflict Set, added new assertions to the original knowledge set, and modified other assertions affected by new assertion, so it could satisfy the open world assumption.

Key words: Description logic, Assertion, Open world assumption, Standard negative paradigm, Determined set