QVT14 — QVTr : Lack of clarity on use of top relations in where clauses

The QVTr specification does not clarify if top relations can be called from where clauses. It would seem to be a source of potential errors if top relations were both explicitly invoked from where clauses and implicitly invoked by the usual mechanism for top relations. An explicit call R(a,b) of a top relation would normally be redundant because R would be attempted on the source element a in any case through the normal mechanism.

The clause should additionally state "Top level relations cannot be invoked from a where clause". As a consequence, primitive domains are only needed in non-top relations (clause 7.2.4 can state that primitive domains should only appear in non-top relations).