An overview of metal-level architectures for control in expert systems

The author argues in favour of the technique of meta-level programming for building expert systems, and discusses a number of different architectures that can be used to implement meta-level systems. In Section 1 the concept of meta-level programming is explained in the context of general programs. Section 2 discusses why expert systems in particular benefit from this technique. Section 3 categorises the meta-level expert systems in the literature on the basis of some of their crucial architectural features and the different types of architectures are compared in Section 4. The author argues in favour of one particular type of meta-level system, the meta-level inference systems. A few open problems associated with meta-level inference systems are discussed, and practical experience with such a system is reported.