Optative Reasoning with Scenario Semantics

The scenario semantics of extended logic programs builds upon simple primitive notions and has been shown to encompass many important logic program semantics. Here we introduce into the scenario semantics paradigm a general exible notion of optative acceptance of acceptable hypotheses, and proceed to illustrate its application to fault diagnosis, taxonomic reasoning, and declarative logic program debugging. Whereas the contradiction removal semantics approach has been shown applicable to a wide range of non-monotonic reasoning problems including the above, it is based either on minimally or on sceptically taking back the most primitive (closed world) assumptions contributing to contradiction. In contrast, we show here how to achieve the same eeect, and solve the same range of problems, by means of a contradiction avoiding rule of op-tative acceptance of hypotheses, easily deened in the present more general approach. Our counterpart to minimality in contradiction removal consists (quasi{complete) scenaria accepting all acceptable optative hypotheses short of contradiction. Our counterpart of contradiction removal scepticism consists in accepting all but only those hypotheses common to all such quasi{ complete scenaria. The close relationship to contradiction removal allows us to rely on our latter's implementation for expeditiously computing results.