Defaults and Revision in Structured Theories

Starting from a logic which speci es how to make deductions from a set of sentences (a ` at theory'), a way to generalise this toa partiallyordered bag ofsentences (a `structured theory') is given. The partial order is used to resolve con icts. If occurs below then is accepted only insofar as it does not con ict with . We start with a language L, a set of interpretations M and a satisfaction relation M L. The key idea is to de ne, for each structured theory, a pre-order on interpretations. Models of the structured theory are de ned to be maximal interpretations in the ordering. They are shown to exist if the logic hL;M; i is compact. A revision operator is de ned, which takes a structured theory and a sentence and returns a structured theory. The consequence relation has the properties of weak monotonicity,weak cut and weak re exivity with respect to this operator, but fails their strong counterparts.

• Type: Conference
• Year: 1991
• Where: LICS
• Authors: Mark Ryan
• Keywords: Automated Reasoning, LICS 1991, Partial Order, Structured Theory, Toa Partiallyordered Bag