Augmenting the Rules

We have so far described MYCIN largely in terms of its knowledge base and inference mechanism, and specifically in terms of rules and a rule interpreter that allow high-performance problem solving. In Chapters 27 through 29 we describe additional knowledge structures that increase the flexibility and transparency of' MYCIN's knowledge base. We refer to many of these as meta-level knowledge. When we speak of meta-level knowledge we mean nothing more than knowledge about knowledge. In a computer program it needs to be represented and interpreted in order to be useful, but the main idea is that it can be an explicit, and flexible, element of expertise. For example, metalevel knowledge can help in modifying an existing rule and in integrating the modification into the whole rule set because it provides additional information about the existing rules to the editor. The ideas for using meta-level knowledge in MYCIN grew out of several projects that Randy Davis was working on in the mid-1970s.