Application Schemes of Possibilitytheory

In this paper, we analyze the formalism proposed by Yagerr6] to represent default knowledge in the framework of possibility theory. Three diierent application schemes are examined. The results produced by these application schemes are compared with those by Reiter's default logic. It is shown that for a restricted class of default theories, there is some kinds of correspondence between Yager's formalism and Reiter's default logic. It is also exempliied that there is much mismatch between them for general default theories. Finally, the xed point mechanism is suggested as an auxiliary scheme to eliminate such mismatch.