| Abstract | We take a tour of various themes in default reasoning, examining new ideasas well as those of Brachman, Delgrande, Poole, and Schlechta. An
underlying issue is that of stating that a potential default principle is
not appropriate. We see this arise most dramatically as a problem in an
attempt to formalize what are often loosely called "prototypes", although
it also arises in other formal approaches to default reasoning. Some
formalisms in the literature provide solutions but not without costs. We
propose a formalism that appears to avoid these costs; it can be seen as a
step toward a population-based set-theoretic modification of these
approaches, that may ultimately provide a closer tie to recent work on
statistical (quantitative) foundations of (qualitative) defaults([1]).
Our analysis in particular indicates the need to resolve a conflation
between use and mention in many default formalisms. Our treatment proposes
such a resolution, and also explores the use of sets toward a more
population-based notion of default.
(Also cross-referenced as UMIACS-TR-96-61)
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