Propositional and terminological knowledge representations

Formalisms based on a propositional representation demonstrate a high representational competence because of their flexibility, properties, and their great expression power, even if they often fail to represent the meaning of the nodes that make up the propositional networks. The presence of a network of definitions would make the representation richer, and would augment the expressiveness and the inferential capabilities of the whole system: the twofold architecture of the hybrid systems seems to be suitable to satisfy these prerequisites. Nevertheless, the hybrid systems fail to clearly define the intensional and extensional levels of knowledge. This paper proposes a different distribution of tasks between the two parts of a hybrid system on the ground of a precise distinction among intensional, mental extensional, and extensional aspects of knowledge. Moreover, it suggests employing a propositional approach also for arranging the abstract definitions of the terminological box. These principles have been tested in KRAM (Knowledge Representation for Agency Modelling), a hybrid system used as a component both of a cooperative interface and of a system able to model actions and minds of cognitive agents.