Summary: Strategies for Semantical Contractions
J¨ urgen Giesl 1 and Ingrid Neumann 2
1 Dept. of Computer Science, Technical University Darmstadt, Alexanderstr. 10,
64283 Darmstadt, Germany, Email: giesl@inferenzsysteme.informatik.th­darmstadt.de
2 Dept. of Computer Science, University of Karlsruhe, Kaiserstr. 12,
76128 Karlsruhe, Germany, Email: neumann@ira.uka.de
The Logic of Theory Change developed by Alchourr'on, G¨ ardenfors and Ma­
kinson (AGM) is concerned with the revision of beliefs in the face of new and
possibly contradicting information. This nonmonotonic process consists of a con­
traction and an expansion transforming one set of beliefs into another. Beliefs are
represented by consistent deductively closed sets of formulas. To achieve mini­
mal change AGM suggested widely accepted postulates that proper contractions
have to fulfill.
In practical applications, e.g. knowledge representation, deductively closed
sets of formulas have to be representable in a finite way. Therefore our main
interest is in finite contractions, i.e. contractions that transform sets of formulas
possessing a finite base into finitely representable sets again.
We have formulated a semantical characterization of finite contractions sa­
tisfying the AGM­postulates which provides an insight into the true nature of
these operations and shows all possibilities to define concrete functions of this

Source: Ábrahám, Erika - Fachgruppe Informatik, Rheinisch Westfälische Technische Hochschule Aachen (RWTH)

Collections: Computer Technologies and Information Sciences