Updated Sept 7 2008: created
First note that there really are no good definitions of business rule methodology available - the main link is to Wikipedia's definition of business rules, where they state simply "Business Rules Methodology is the process of capturing business rules in English, in real-time while empowering users to manage rules with a few simple steps". What are the simple steps that empowering users to manage rules ? And do they really have to be in English ?
Here is a ragbag of definitions for "methodology".
So a definition of business rule methodology would be something like "a practical, proven and documented process for analyzing, designing and implementing business rule systems".