Abstract
Graphical representations have been successfully used during the knowledge acquisition sessions, as a medium of communication between the knowledge engineer and the domain expert. In this paper we present a model for a graphical representation of knowledge in a knowledge-based system, and a direct reasoning mechanism over this representation. Having the knowledge represented graphically allowed us to borrow some techniques from Truth Maintenance Systems like caching reasoning and dependency directed backtracking. The issues raised in this research are illustrated by a prototype implementation system developed using visual C++ which was used for diagnosing plant diseases in the domain of agriculture.