1. A method of simulating an execution of a knowledge base and displaying the simulation of said knowledge base on a display of a computer, said method comprising the steps of: selecting a set of one or more statements of said knowledge base; representing, by said computer, each statement from said set by a node on said display; simulating an execution of said knowledge base; and when, during said simulating step, an evaluation of any one of said statements of said set is being simulated, marking the respective node on said display by said computer as the node representing the statement whose evaluation is being simulated.