[qvtd-dev] QVTi Guard Pattern Assignments

[Ed Willink <ed@xxxxxxxxxxxxx>]

Hi Horacio

I'm having two problems with the 'decision' that ":=" in guard patterns 
is relized by a variable initializer in the AST.

a) my CG makes a mess of them (just needs debugging)
b) OCL validation complains about type errors

If we look at some original QVTc

map primitiveAttribute in umlRdbms refines attributes {
    check enforce uml (t:PrimitiveDataType |) {
        a.type := t;
    }

we see a Bottom pattern predicate. But in QVTi it contributes to:

map classPrimitiveAttributesLM in umlRdbms {
    uml (c:Class, t:PrimitiveDataType, a:Attribute |
        a.owner = c;
        --getAllAttributes(c)->includes(a);
            t := a.type;
        ) {
        }

a Guard Pattern Variable Assignment.

The QVT spec is very vague on VariableAssignments but is clear that 
PropertyAssignments are bottom pattern only.

The translation to QVTi is really a predicated assignment

a.type.oclIsKindOf(PrimitiveDataType)
t := a.type

so perhaps we define this as the semantics of the Guard VariableAssignment.

t := a.type

avoiding the conflict with the OCL CompatibleVariableInitializer constraint.

Allowing a VariableAssignment in a GuardPattern is a bit of a mess since 
CorePattern.bottomPattern is meaningless.

Easier to introduce a new VariablePredicate class (for QVTi only).

Does this make sense?

    Regards

        Ed