During the quarter century since the birth of "artificial intelligence" (Al), attempts to develop symbolic models of human reasoning processes have been a major focus of the ongoing research. It is only in the last half-dozen years or so, however, that several related Al research themes have come together in the formation of what is now known as "expert systems researoh" CI], In this brief paper I would 1.ke to review the key aspects of A: and expert syste-.s

Reserved Function Names 109 Appendix Ili.

Programs Based on the Blackboard Model 8 2.2.1.

"Learning", the incorporation of additional knowledge into expert systems, ranges from human data entry (learning by being told), to data gathering (learning by observing), to full-fledged theory formation (learning by discovery). One important kind of learning is the compiling of descriptive meta-knowledge into strategic form, recasting it into a form in which it can be evaluated efficiently. Much of what we earlier called strategic meta-knowledge may be seen to be operationalized "caches" of descriptive or systemic meta-knowledge. For instance, R9 and R10 can be converted from systemic to strategic form by slight rewordings of their actions.

Search 4. Methods for assigning credit and blame--obtaining a local Performance Standard

This manual describes a domain-independent system, called EMYCIN, for constructing one class of expert computer programs: rule-based consultants. The resulting programs use knowledge specific to a problem domain to provide consultative advice to a client. The system-building tool, EMYCIN, is based on the domain-independent core of the MYCIN program. Domain kno,./ledge is represented in EMYCIN systems primarily as production rules, which are applied by a goal-directed backwardchaining control structure. Rules and consultation data may have associated measures of certainty, and incomplete data entry is allowed. The system includes an explanation facility that can display the line of reasoning followed by the consultation program, and answer questions from the client about the contents of its knowledge base. To aid the system designer in producing a knowledge base for a domain quickly and accurately, EMYCIN provides the following features: (1) a terse.

This paper presents an "expert system" devised to aid organic chemists in determining the structure (i.e. the arrangement of atoms and bonds) of newly isolated, naturally occurring compounds. The system exploits a data base of rules for analyzing.013 C nuclear magnetic resonance spectra" [2. 13 C spectroscopy is a relatively new technique; only in the last ten years, at most, has this analytic approach been practical. Currently, no general interpretive schemes exist for thoroughly analyzing 13C spectra. A few limited classes of compounds have been investigated in detail, and highly specific schemes for interpreting their 13C spectra have been developed. The only generally applicabl- "interpretation rules" rely on correlation J of spectral and substructural features.

We describe an oncology protocol management system, named ONCOCIN, that is designed to assist physicians in the treatment of cancer patients. The system is a set of related programs, one of which is a rule-based reasoner that encompasses the necessary knowledge of cancer chemotherapy. Representation and control techniques are dizcussed, and ONCOCIN is contra7ted with:qstems that could be built using EMYCIN. Of particular Interest is the need to provide ONCOCIN with an interface that will make the system acceptable to oncologists.

We describe a program for verifying that a set of rules in an expert system comprehensively spans the knowledge of a specialized domain. The program has been devised and tested within the context of the ONCOCIN System, s rule-- based consultant for clinical oncology. The stylized format of ONCOCTN's rules has allowed the automatic detection of a number of common errors as the knowledge base has been developed. This capability suggests a general mecharism for correcting most problems with knowledge base completeness and consistency before they can cause performance errors.

The Key idea is to represent explicitly and separately: a A. The limitations of MYCIN for application to teaching domain-independent diagnostic strategy in the form of meta-rules,