Metric: The developer should provide a description of the theory and method of translation used by the system. -- Method: Provision of supporting documentation such as white papers. -- Scale: Percentage of conformance. --
There is a variety of each type of system but especially so with respect to rule-based systems.
Generally, it is assumed that a theoretically sound system is easier to use, manage, update, etc. than one that is not theoretically based.
As important as current coverage is a systems capacity for update and improvement.
Many of the techniques used in verification of particular models tend to be glass-box, that is, isolating an element of the system, or potentially examining source code and data files.