The architecture and control strategies of computing environments able to provide decision-support, together with software selection, are described. In the area of engineering design, the need to provide both a knowledge base and a database, and direct communication between the two, is recognised as an essential pre-requisite to the successful development of decision-support software. The role of expert systems in developing and maintaining the knowledge base, and factors influencing the choice of expert system, are discussed. An integrated software network in which to build computer-aided design tools is described and fully realised. The network is based on Crystal, a commercially-available expert system shell, and Lotus 123, which provides data support and management. The expert system can interrogate directly the database via a custom interface while a second interface allows the user direct access. Library facilities are also available to permit the filing of designs produced by the system. Assessment of the interface is achieved by comparing it with a commercially-available database interface. Finally, using the software network developed, two rule-based expert decision-support systems for the design of power transformers and inductors carrying direct current, operating at frequencies up to 100 kHz, are developed. The relevant component-design methodology, and the scope and operation of the design software, are explained.