ABSTRACT
The propositional models reviewed in the previous chapter were principally concerned with representing declarative knowledge-that is, knowledge of facts about the world. This chapter will be concerned with two models of procedural knowledge-knowledge about how to do something. These two models are stimulus-sampling theory (Estes, 1959) and the Newell (1973) PS system. The distinction between declarative and procedural knowledge is analagous to the computer science distinction between program and data. Any complete psychological model obviously needs both types of knowledge. However, there is room for disagreement about what to represent procedurally and what to represent declaratively. Both theories reviewed in this section have opted for representing most knowledge in a procedural format. In contrast, ACT makes what might be called an "even division" between representing information procedurally and representing information declaratively. There is also room for disagreement about how different the formalisms should be that represent declarative and procedural knowledge. Norman and Rumelhart (Section 2.4, this volume) opted for a system in which there are no formal differences between the representations for the two types of knowledge. In contrast, ACT will opt for a system which makes a fundamental distinction between the representations for these two types of knowledge.
