Updated Oct 6 2008: fixed bad links and added more links
Barbara Von Halle is a true pioneer in the discipline of business rules. She started with a series of important articles about business rules in Database Programming and Design magazine in the early 1990s and then just kept going. She founded Knowledge Partners International in 1996.
She wrote what is perhaps the best single text on business rules, Business Rules Applied: Building Better Systems Using the Business Rules Approach.
She was also a major contributor to the classic Defining Business Rules - What Are They Really?.
Also notable is us her recent book Business Rule Revolution: Running Business the Right Way, with Larry Goldberg and John Zachman.
She is chairing the 2007 Business Rules Symposium this year.