What would you use for a business validation layer?

Question

In my project I need to create a business object validation layer that will take my object and run it against a set of rules and return either pass or fail and it's list of failure reasons. I know there are quite a few options out there for accomplishing this.

From Microsoft:

• Enterprise Library Validation Application Block
• Windows Workflow Foundation Rules Engine

Open Source:

• Drools.NET
• Simple Rule Engine(SRE)
• NxBRE

Has anyone had any particularly great successes or failures with any of these technologies (or any that I didn't list) or any opinions on what they feel is best suited for business rules validation.

Edit: I'm not just asking about generic validations string length < 200, zip code is 5 digits or 5+4 but assume that the rules engine would actually be leveraged.

Answer 1

The code-versus-rules-engine decision is a matter of trade-offs, IMHO. A few examples are:

Advantages of code

• Potentially higher performance.
• Uses developers' existing skills.
• No need for separate tools, run-time engines, etc.

Advantages of rule engine

(Features vary across the various rule engines.)

• Rule DSL that is writable (or at least readable) by business users.
• Effective- and expiration-date properties that allow automatic scheduling of rules.
• Flexible reporting from rule repository supports improved analysis and auditing of system behavior.
• Just as data-base engines isolate data content/relationship issues from the rest of the system, rules engines isolate validation and policy from the remainder of the system.