Summary

As with scripting languages, knowledge of a rule-based language is a valuable skill that software engineers should have at their disposal. Rule-based programming is no longer considered purely the domain of the computer scientist but is finding an application in the development of business systems.

Business rules represent one of the greatest areas of complexity within enterprise systems, and the rule engine offers an effective mechanism for managing their sophisticated and dynamic nature. Rule engines are therefore well suited to rapid application development, offering the following benefits:

• Rules can be externalized from all applications to a centralized repository where they can be managed using specialized rule management tools.

• Rule-based programming languages are more suited to defining business rules than are languages such as Java.

• Business rules can be defined and managed by domain experts rather than by skilled IT professionals.

• The rules themselves are dynamic, enabling business-rule changes to be effected across the enterprise without the need to rebuild system components.

The next and final chapter on rapid development languages covers aspect-oriented programming, one of the software industry's most exciting new paradigms.

Additional Information

The CLIPS software, along with examples and tutorials, is available from the site http://www.ghg.net/clips/CLIPS.html.

Jess is not public domain software. However, numerous Java implementations of rule engines exist that are. Table 10-1 lists some of them.

Table 10-1. Open Source Java Rule Engines

Name	Reference
Drools	http://drools.org/
OFBiz Rule Engine	http://www.ofbiz.org/docs/rules.html
Algernon	http://algernon-j.sourceforge.net/
TyRuBa	http://tyruba.sourceforge.net/
JTP Java Theorem Prover	http://www.ksl.stanford.edu/software/JTP/
JEOPS, Java Embedded Object Production System	http://www.di.ufpe.br/~jeops/
InfoSapient	http://info-sapient.sourceforge.net/
JShop	http://www.cs.umd.edu/projects/shop/description.html
RDFExpert	http://public.research.mimesweeper.com/RDF/RDFExpert/Intro.html
Jena 2	http://www.hpl.hp.com/semweb/jena2.htm

For more information on the intricacies of the Rete algorithm, refer to the paper in which it was first defined, Rete: A Fast Algorithm for the Many Pattern/Many Object Pattern Match Problem by Charles L. Forgy [Forgy, 1982].