Infobase Change: A First Approximation

  • Authors:

  • Thomas Andreas Meyer;Willem Adrian Labuschagne;Johannes Heidema

  • Affiliations:

  • Department of Computer Science, University of Pretoria, Pretoria 0002, South Africa tmeyer@cs.up.ac.za;Department of Computer Science and Information Systems, University of South Africa, Box 392, Pretoria 0003, South Africa, E-mail: labuswa@alpha.unisa.ac.za;Department of Mathematics, Applied Mathematics and Astronomy, University of South Africa, Box 392, Pretoria 0003, South Africa, E-mail: heidej@alpha.unisa.ac.za

  • Venue:
  • Journal of Logic, Language and Information
  • Year:
  • 2000

  • Basic Infobase Change

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  • Non-prioritised ranked belief change

    TARK '01 Proceedings of the 8th conference on Theoretical aspects of rationality and knowledge

  • Merging epistemic states

    PRICAI'00 Proceedings of the 6th Pacific Rim international conference on Artificial intelligence

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Abstract

Generalisations of theory change involving operations on arbitrary sets ofwffs instead of on belief sets (i.e., sets closed under a consequencerelation), have become known as base change. In one view, a base should bethought of as providing more structure to its generated belief set, whichmeans that it can be employed to determine the theory contraction operationassociated with a base contraction operation. In this paper we follow suchan approach as the first step in defining infobase change. We think of an infobase as a finite set of wffs consisting of independently obtainedbits of information. Taking AGM theory change (Alchourrón et al. 1985) as the general framework, we present a method that uses the structure of aninfobase B to obtain an AGM theory contraction operation for contractingthe belief set Cn(B). Both the infobase and the obtained theory contraction operation then play a role in constructing a unique infobasecontraction operation. Infobase revision is defined in terms of an analogueof the Levi Identity, and it is shown that the associated theory revisionoperation satisfies the AGM postulates for revision. Because every infobaseis associated with a unique infobase contraction and revision operation, the method also allows for iterated base change.