Fourteenth Annual IEEE Symposium on

Logic in Computer Science (LICS 1999)

Invited Talk: Plausibility Measures and Default Reasoning: An Overview (at LICS 1999)

Authors: Nir Friedman Joseph Y. Halpern


We introduce a new approach to modeling uncertainty based on plausibility measures. This approach is easily seen to generalize other approaches to modeling uncertainty, such as probability measures, belief functions, and possibility measures. We then consider one application of plausibility measures: default reasoning. In recent years, a number of different semantics for defaults have been proposed, such as preferential structures, epsilon-semantics, possibilistic structures, and kappa-rankings, that have been shown to be characterized by the same set of axioms, known as the KLM properties. While this was viewed as a surprise, we show here that it is almost inevitable. In the framework of plausibility measures, we can give a necessary condition for the KLM axioms to be sound, and an additional condition necessary and sufficient to ensure that the KLM axioms are complete. This additional condition is so weak that it is almost always met whenever the axioms are sound. In particular, it is easily seen to hold for all the proposals made in the literature. Finally, we show that plausibility measures provide an appropriate basis for examining first-order default logics.


    author = 	 {Nir Friedman and Joseph Y. Halpern},
    title = 	 {Plausibility Measures and Default Reasoning: An Overview},
    booktitle =  {Proceedings of the Fourteenth Annual IEEE Symp. on Logic in Computer Science, {LICS} 1999},
    year =	 1999,
    editor =	 {Giuseppe Longo},
    month =	 {July}, 
    pages =      {130--135},
    location =   {Trento, Italy}, 
    note =       {Invited Talk},
    publisher =	 {IEEE Computer Society Press}