[rules-users] How to do validation of facts in a Stateful Session?

Hi there, My project uses Drools to (among other things) validate new facts/updates to old facts, according to a set of rules. (For example, we might have a rule that says "No two people can be named the same thing".) Our method of validation and error reporting was originally chosen for a stateless session (before we had the requirement of doing checks like the above), and I feel I've had to hack it a bit much to get it working with stateful sessions. The current methodology is: 1. (Website) The user inserts/updates a fact. 2. (Java) If the fact is new, an object is created for it. If it is an update, the pre-existing object is fetched from the object repository (the interface to the database) and a backup copy of the object is taken. 3. (Java) This fact is either inserted into the KnowledgeBase (KB) or a pre-existing fact in the KB is updated depending. 4. (Rules) If the new/updated object fails a validation rule, it will be retracted and a ValidationError object will be inserted into the KB. 5. (Java) The code then searches for ValidationError objects that match the just inserted/updated object. If it finds any it records them and then retracts them from the KB. 6. (Java) If there are no errors, then that's it - a success report is generated and passed back to the website. 7. (Java) If there were errors, then if the user was updating a fact the backup of it (before the changes) is inserted back into the KB. The website is then passed a failure report. It just feels very hacky to do so much manual insertion/retracting from the Java side of the code. So, is there a 'correct' way to do stateful validation? And does our current way even work, or are there hidden problems that we've not spotted? Cheers, Stephen -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.