Verification and WF (not WWF - that's copyrighted by the World Wildlife Foundation) address quite different problems and are complimentary technologies.

The fact that both are 'rule-driven' is the source of much confusion. Here's my high level overview of the comparison.

• Verfication (Validation) rules pass judgement: is this valid or not?
• Workflow rules govern process transitions: where do I go from here given the present conditions?

WF is great for transitions but is completely inappropriate for validation. You will not find any examples of WF validation in any serious WF book. You might find something that combines validation with a state transition, but not something dedicated to validation per se.

Moreover, WF is focused on long-running transitions: "I can't go forward with this order until my manager approves it ... which could take hours, days, weeks." It is much too heavy-weight for the synchronous transitions of an application such as "when I click the forward button, I move to the next screen of the wizard."

There are other 'rule-driven' systems that interest us as well:

• Security guards object and value access: do I have the authority to see this property or object? may I update (or delete) it?
• Transformation rules: pass the property value through this translation filter before returning it

The latter are candidates for plug-ins into our get and set interceptors.