Comment by dkimball

Alex Papadimoulis of the Daily WTF has an article on this -- it's his opinion that the simple, "bone-headed" approach is the best one for constraints like this, and homegrown business rule engines are dangerous:

http://thedailywtf.com/Articles/Programming-Sucks!-Or-At-Lea...

However, commercial business rule engines might work out better, provided they stick to XML or known formats of I/O in general.