A good model must be an accurate representation to the appropriate level of abstraction.

A good model must be a complete representation within the chosen scope.

Scott Ambler gives the following characteristics for agile models that seem reasonable for any model:

* fulfills its purpose

* is understandable to its audience

* is sufficiently accurate

* is sufficiently consistent

* is sufficiently detailed

* provides positive value

* is as simple as possible

Scott Anbler. Just Good Enough. Dr. Dobb's Journal, Dec 16, 2004.