How could a shell improve the maintainability of expert systems?

The author points out two important areas in which next-generation expert system shells could contribute to alleviate some of the problems associated with the maintenance of large expert systems: (1) supporting the development of a consistent domain model, and (2) improving the structure and the modularity of the rule base. The knowledge base of an expert system consists of a model of the problem domain and a description of the system´s problem solving behavior. The maintainability of a knowledge-based system thus depends on a good design of both components. An example of a shell that exhibits some of the capabilities described here is CLASP