For almost two years now, I've been intending to write an article about the mysterious 'side effects' flag used in Microsoft Business Rule Engine policies. Microsoft documents this feature (see http://msdn2.microsoft.com/en-us/library/aa559124.aspx), and describes very briefly how to control it. The mystery that surrounds this flag arises because it is represented by an attribute named 'sideeffects' in Microsoft's BRL (Business Rule Language) although it actually controls a caching mechanism,