Knowledge representation, major

Implementation tools differ in the facilities they offer. A major selection criterion is the knowledge representation possibilities the tools offer. Another important issue is the access to external programs. This is an important aspect for chemical knowledge bases since many chemical problems involve a large computational aspect that is best solved by an external, algorithmic program. 

Demons and Variables. ALEX provides a three-tiered knowledge representation structure of contexts, demons, and variables. Contexts are top-level structures that isolate individual major areas of the problem under analysis. Demons are the central knowledge representation structure they are essentially frame-based information storage nodes with slots both to hold information on the content of the demon and to reflect the impact of one or more variables on the status of the demon. Variables may hold user-input, default, or calculated information. 

Separation of the reasoning component from other components of the system has proved to have many advantages (8-10). It has allowed us to experiment with different representations of chemical knowledge without major changes in the overall system. The design has also allowed us to easily add or delete knowledge from our data base, and has given us the potential to interface with a wide variety of commercial data bases such as those provided by the Institute of Scientific Information and Chemical Abstracts. 

A major result from using object-oriented approaches is that we obtain the sort of knowledge representation structures that are commonly found in many expert systems. Thus, object-oriented... 

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