An Analysis of Defeasible Inheritance Systems

We give a conceptual analysis of (defeasible or nonmonotonic) inheritance diagrams, and compare our analysis to the ”small/big sets” of preferential and related reasoning. In our analysis, we consider nodes as information sources and truth values, direct links as information, and valid paths as information channels and comparisons of truth values. This results in an upward chaining, split validity, off-path preclusion inheritance formalism. We show that the small/big sets of preferential reasoning have to be relativized if we want them to conform to inheritance theory, resulting in a more cautious approach, perhaps closer to actual human reasoning. Finally, we interpret inheritance diagrams as theories of prototypical reasoning, based on two distances: set difference, and information difference. We will also see that some of the major distinctions between inheritance formalisms are consequences of deeper and more general problems of treating conflicting information. AMS Classification: 68T27, 68T30

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