**Dept. of Computer and Information science, Linköping University**

## IDA Technical Reports: abstract

*Generated: Wed, 20 Sep 2017 09:37:24 *

Doherty, P., Driankov, D., and Hellendoorn, H. (1992).
** Fuzzy
If-Then-Unless Rules and their Implementa tion**.
Technical Report LiTH-IDA-R-92-21, Department of Computer and Information
Science, Linköping University, Sweden.
Extended Version of a Paper accepted at InternationalConference on Information
Processing and Management of Uncertainty in Knowledge-Based Systems, IPMU'92
Palma de Mallorca, July 6-10, 1992.
(bibtex),

**Abstract: **We consider the possibility of generalizing the
notion of a fuzzy If-Then rule to take into account its context dependent
nature. We interpret fuzzy rules as modeling a forward directed causal
relationship between the antecedent and the conclusion, which applies in most
contexts, but on occasion breaks down in exceptional contexts. The default
nature of the rule is modeled by augmenting the original If-Then rule with an
exception part. We then consider the proper semantic correlate to such an
addition and propose a ternary relation which satisfies a number of intuitive
constraints described in terms of a number of inference rules. In the rest of
the paper, we consider implementational issues arising from the unless
extension and propose the use of reason maintenance systems, in particular
TMS's, where a fuzzy If-Then-Unless rule is encoded into a dependency net. We
verify that the net satisfies the constraints stated in the inference schemes
and conclude with a discussion concerning the integration of qualitative
IN-OUT labelings of the TMS with quantitative degree of membership labelings
for the variables in question. A generalization to the TMS relabeling
algorithm is proposed which would permit the modeling of reasoning with
``generalized modus ponens''.

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