40. The method of claim 32 , wherein the one or more rules are registered with a unit that applies the one or more rules to the value to determine if the value is valid.
32. A method comprising: registering one or more rules associated with an entity of a model, the one or more rules related to one or more attributes of the entity; receiving input specifying a value for an attribute of the entity; applying the one or more rules to the value to determine if the value is valid; and generating, using a processor, a validation result that indicates whether the value is valid based on the applying.