10. A tangible computer-readable storage medium storing computer-executable instructions for execution by a processor, the medium storing one or more instructions for: defining one or more rules for validating or inferring a value of an attribute associated with an entity of a model, or registering one or more rules with a unit that validates or infers the value; and validating or inferring the value based on the one or more defined or registered rules.
10. A tangible computer-readable storage medium storing computer-executable instructions for execution by a processor, the medium storing one or more instructions for: defining one or more rules for validating or inferring a value of an attribute associated with an entity of a model, or registering one or more rules with a unit that validates or infers the value; and validating or inferring the value based on the one or more defined or registered rules. 20. The medium of claim 10 , further comprising one or more instructions for: identifying a conflict in the one or more defined or registered rules.