Strong and Default Negation in Defeasible Logic Programming
Alejandro Javier García, Guillermo Ricardo Simari · 2004
Defeasible Logic Programming [8] (DLP) is an extension of Logic Programming capturing common-sense reasoning features, that are difficult to express in traditional Logic Programming. The presented language can manage defeasible reasoning, allowing the representation of defeasible and non-defeasible knowledge. A defeasible logic program is defined in terms of two disjoint sets of rules: a set of strong rules for representing strict (sound) knowledge, and a set of defeasible rules for representing tentative information. In DLP, a query q will succeed when there is an argument A for q that is a justification for q. Building a justification involves looking for counterarguments that could be defeaters for A. Since defeaters are arguments, there may exist defeaters for the defeaters, and so on, thus requiring a dialectical analysis. DLP considers two different negations: strong negation, which is represented by the symbol “∼” which is used for representing contradictory knowledge; and, default negation, represented by the symbol “not” used for representing incomplete information. In this work, we will show why two types of negations are needed, the differences between them, some properties, and how they could be combined to take advantage of the full expressiveness of the language.