OCL25 — OCL Constraint violation messages

OCL supports definition of constraints, but it is difficult for tools to offer better error messages to a user than 'Constraint <constraint-name> violated for <constrained-element-name>'.

It would be helpful if Constraints had an additional String-valued expression to be evaluated in the context of the error, so that tools could evaluate it and present the result to the user.

Suggest add an optional argument to the (not-optional) constraint name. e.g.

inv ConstraintName('Unable to find ' + self.target.name): ...