|
Abstract : |
In this paper, we present a shell for hybrid knowledge representation. This system supports three dierent knowledge representation formalisms: First-order logic, terminological language and semantic networks. The rst-order logic formalism allows the representation of assertional knowledge in the form of logic formulae, and the calculation of an entailment relation that, although weaker than the usual logic implication, has the advantage of being decidable. The terminological language allows the denition of concepts and n-valued relations between these concepts through the use of description primitives. These primitives include disjunction and negation, besides special symbols for the universal and empty entities. This formalism also supports the calculation of subsumption between entity descriptions. Finally, the semantic network formalism allows the denition of hierarchies of classes and the calculation of inheritance with exceptions. The system automatically supports hybrid inferences taking into account the knowledge represented in dierent formalisms. All the algorithms involved in the inferences supported by the system are decidable, and have the property of being sound and complete according to a four-valued semantics. Besides these facilities the shell allows the user to represent procedural knowledge of a domain using the primitives embedded at the heuristic level. The system has been implemented in Common Lisp, and makes use of an object-oriented extension for this language., |
