Understanding expert systems maintenance

An approach the design of maintainable expert systems is presented. Central to this approach is a conceptual model in which the data and knowledge are both modelled as formal “items” in a uniform way. “Objects” are introduced as “item building” operators. The notion of the “decomposition” of items and objects provides the foundation for a single rule of normalisation. This single rule applies to all items and objects, including knowledge items, and is a non-trivial generalisation of the traditional normal forms for database. Coupling relationships represent the necessary maintenance paths in the conceptual model. A complete characterisation of coupling relationships is given, and the value of normalisation to the reduction of maintenance costs is discussed.