1. A method for operating a computer to update an entity-relationship model database, the method comprising the steps performed by the computer of: accepting data for a new or modified instance or to delete an instance of an entity; activating constraints applicable to the accepted data; determining a firing order including at least a first constraint for firing from among the activated constraints, the first constraint being determined based on criteria which attempts to identify a constraint most likely to be violated; firing the first constraint; determining if the first constraint was violated; and returning to the step of activating constraints if any constraints remain to be fired.