Integrating Marker-Passing and Problem-Solving
The diagram presented earlier of a system integrating a problem-solver and a marker-passer is reproduced here as Figure 13. To review: The basic flow of control is th a t the problemsolver attem pts to achieve a goal given a set of initial conditions. As the problem is solved the marker-passer spreads activation from items being examined in the problem-solving effort. When paths among these items are found, they go to the path evaluator, which examines these paths looking for certain patterns. If these patterns are found, information is added to the memory to help direct the remainder of the problem-solving task. I t is easiest to describe these steps as occurring in series, although better performance is of course achieved when they are performed in parallel. This chapter seeks to expand the description given so far and to present the details of this organizational scheme by presenting the program SCRAPS and explaining how it works. In essence, SCRAPS is viewed as the “working prototype” of this sort of system. This may cause a slight blurring of the distinction between the idea “ integrating a problem-solver with a markerpasser” and the im plem entation “SCRAPS.” Where this distinction is im portant, we will try to make it clear which we are referring to.