Chapter 10. Working to Rule

A recurring theme of this book is that rapid development is achievable by being able to quickly and effectively accommodate change. One area of most applications that is subject to continual change throughout the life of the system is the business rule.

This chapter examines the benefits of applying rule-based languages and rule-engine technology to the problem of constantly mutating business logic. Specifically, this chapter covers how rule engines can assist in rapid application development by:

• Enabling the description of rules in a language appropriate for expressing complex business knowledge.

• Improving system maintainability by cleanly separating business logic from application logic.

• Allowing the definition of business-rule sets as an enterprise resource, thereby enabling business rule changes to be swiftly effected across all corporate systems.

• Providing sophisticated end-user tools for visually specifying business logic.

We cover some of the main concepts behind rule-based programming by introducing the expert system shell language Jess, a rule engine specifically designed for writing rule-based systems for the Java platform.