Expert systems: they ain´t what they used to be

It is argued that expert systems have evolved from early forays into the essence of intelligence and from proof-of-concept systems based on toy problems into robust, operational systems, with all of the same problems facing mature software developed conventionally. During this evolution, some architectural concepts have been developed that are still valid and offer methods for general implementation to avoid problems that obstructed the earliest attempts. Some of these systems, their goals and important architectures are described. The sonar expert system (SES) evolution, originating from the HASP expert system begun in 1973, is used as a case study