Each cycle picks up where the last ended, building on the prior rule set. For a developer, the spiral represents a continuing education process in which more and more of an expert's reasoning knowledge is discovered and formalized in the rule set. Here, each development cycle was presented in terms of seven consecutive stages. Many aspects of traditional systems analysis and project management can be applied to the development of expert systems. Rule set development is a process of discovery and documentation.
Research continues in search of ways of automating various aspects of the process.
Until that time comes, the topics discussed in this chapter should serve as reminders to developers of expert decision support systems about issues to consider during the development process. Within each approach, many variations are possible. There are many kinds of reverse reasoning and many kinds of forward reasoning. Because no single kind of reasoning is best in all situations, skilled developers find it valuable to have mechanisms for easily adjusting an inference engine's exact reasoning behavior so it can differ from one consultation to another and from one rule set to another. Such adjustments can help the developer build an expert system whose advice more closely resembles that of the human expert.