This is a good place to start learning abut rule modeling.
This is the basic example illustrated in the online video demo which you can view here:
http://www.corticon.com/Demo/Corticon-BRMS-Enterprise-Demos/Modeling/Cor...
It models the following two seemingly simple rules
Applicants who skydive are high risk
Applicants under 35 have low risk
Using Corticon's built in analysis tools you can discover that even these simple rules suffer from ambiguity and incompleteness. Take a look at the attached PDF to get an overview, then download and run the example.
A sample rule model and explanatory notes are available as attachments. When you are logged in you will see the link below.