Artifact Design, Artifact Model, and Artifact Function Specification #444

Should 'Artifact Model' be a subclass of 'Artifact Design'? It is currently, but I don't think so, as artifact designs prescribe objects and artifact models prescribe functions and qualities. This separation of prescriptions of objects and prescriptions of the SDCs those objects have is recognized already by the location of 'Artifact Function Specification' in the hierarchy.

'Artifact Function Specification' also seems to overlap somewhat with the meaning of 'Artifact Model.' So, I'm not sure that both classes are needed in their current form.

That said, even if I'm wrong, the definition of 'Artifact Model' should be changed to reflect the fact that its parent class is 'Artifact Design.'