Is a formal specification complete ?
By `formal' we mean a machine-readable description of what is correct or incorrect behaviour. A complete specification might describe all allowable behaviours and prohibit all remaining behaviours, but most formal definitions today are not complete in this sense. For instance, a definition that consists of a list of safety assertions and a few liveness assertions might still allow all sorts of behaviours that the designer knows are wrong. He can go on adding more assertions, but when does he stop ?
One might define a 'complete specification' as one that describes all observable behaviours. Such a specification does not restrict or prescribe the internal implementation in black box terms since this is not observable.
When evaluating an assertion-based test program for an IP block, we can compute assertion coverage in many ways: e.g. What percentage of rule disjuncts held as dominators (on their own) ?
Or, e.g. What (inverse log) percentage of reachable state space was spanned?