Major Problem:
(1) The current abstract syntax of ImperativeOCL introduces a couple of
unclear situations. This may lead to incompatible QVT implementations.
Further Problems:
(2) Control flow constructs introduced by ImperativeOCL are redundant
compared with existing conventional OCL constructs.
(3) Several OCL equivalence rules break when ImperativeOCL is present.
Detailed problem description:
(1) The current abstract syntax of ImperativeOCL introduces a couple of
unclear situations. This may lead to incompatible QVT implementations.
In the abstract syntax, ImperativeOCL expressions / statements are
inherited from OclExpression. Therefore, conventional OCL
expressions may (and will) contain sub-expressions that are
actually ImperativeOCL expressions.
In conventional OCL, the interpretation of an expression under a
given environment is a value. In ImperativeOCL, the interpretation
of an expression is a value and a new environment
(state,variables). This extended interpretation is not given for
conventional OCL expressions, leading to undefined operational
semantics of those expressions.
Example: Given the following compute expression:
compute(z:Boolean) {
var x : Boolean := true
var y : Boolean := true
if ((x:=false) and (y:=false))

z := y
}
What is the value of this expression: is it true or false (It
depends on whether the 'and' operator is evaluated short-circuit
or strict). The situation is similar for the evaluation of the
other logical connectives, forAll, and exists when these
expressions contain imperative sub-expressions.
(2) Control flow constructs introduced by ImperativeOCL are redundant
compared with existing conventional OCL constructs.
Some of the new language features in ImperativeOCL such as forEach
and the imperative conditional are not really necessary. Their
effect can already be achieved using conventional OCL expressions:
For example:
company.employees->forEach(c)

has the same effect as
company.employees->iterate(c; r:OclAny=Undefined |
c.salary := c.salary * 1.1
)
and
if ( x < 0 )

else

endif is the same as
if x < 0 then x := 0 else x := 1 endif
(3) Several OCL equivalence rules break when ImperativeOCL is present.
In conventional OCL, several equivalence rules well known from
logic hold. Allowing OCL expression to contain imperative
sub-expressions breaks these equivalence rules.
Examples:
let x=e1 in e2 equiv. e2

e1 and e2 equiv. e2 and e1
These equivalences do not necessarily hold if e1 or e2 are allowed
to have side-effects.
Proposed solution:
(A) - (The cheap solution.) State textually that conventional OCL
expressions (as described in the OMG OCL spec.) are not
allowed to have side effects unless used as part of a top
level ImperativeOCL expression. Therefore, even in a system
supporting ImperativeOCL, class invariants, and pre- and
postconditions (e.g.) will not be allowed to contain
ImperativeOCL sub-expressions.
State explicitly that the redundant flow control statements
have been introduced (solely) to write concise imperative
programs and that the side-effect free forms of conditional
evaluation ( 'if-then-else-endif' and 'iterate' ) shall not be
used to program side-effects (instead, the ImperativeOCL forms
shall be used).
(B) - (Major rework.) Rework the abstract syntax to reuse OCL
expressions by composition rather than by inheritance.
Imperative expressions ( => rename to 'statements' ) then may
contain sub-statements and OCL expressions; OCL expressions
are reused unchanged from the OCL spec (no imperative
sub-expressions, no side-effects).
These issues have been discussed on the MoDELS 2008 OCL Workshop,
more details can be found at
http://www.fots.ua.ac.be/events/ocl2008/PDF/OCL2008_9.pdf

QVT Relations and working with stereotypes: Is there something like a QVT-R standard library with methods on stereotypes in it? There is none in the specification; compare QVT-R, there are some methods. Are there some else options for accessing stereotypes with QVT-R?

In 7.11.3.6 (and 7.8) the ordering of parameters is implied but not explicit. Presumably the first is the output (enforced direction) so:

package QVTBase

context TypedModel
def: allUsedPackage() : Set(EMOF::Package)
= self.dependsOn.allUsedPackage()>asSet()>union(self.usedPackage)

endpackage

package QVTRelation

context RelationImplementation
inv RootNodeIsBoundToRootVariable : self.inDirectionOf.allUsedPackage()>includes(self.impl.ownedParameter>at(1).type._package)

endpackage

This is not satisfied by almost the last line of RelToCore in 10.3:

enforce domain core me:OclExpression{} implementedby CopyOclExpession(re, me);

which seems to have output second.

-----------------------------------------------------

More significantly CopyOclExpession(re, me) is not meaningful as a black box signature, since it is a static function and EMOF has no way to define static functions. Perhaps it is a query, for which the declaration was omitted from the example. If this is the case, it should be made clear that black box operations must be declared internally as queries and bound externally to static operations of the transformation.

This semantic clumsiness could be resolved, if, within a transformation,
relation, domain or query, self is bound to a transformation instance. Queries would then be normal non-static operations of the transformation (class) and the implementedBy operation call would be a normal implicit call via self of a non-static transformation operation or query. (A RelationCallExp would also deviate less from OCL than it currently does.) This would also allow a transformation to extend a Utility class that provided the required black box operations. Since queries and relations are declarative, it is not obvious that there need be any prohibition on the content of an extended Class; if the Class has properties, these cannot mutate during a query or relation match, so the properties are ok; they might even permit useful behavioural tailoring. For instance an 'inherited' Boolean mangledNames property could influence the mapping of names between input and output.

The RelToCore example can then be mended by declaring that:

RelToCore(...) extends utils::CopyUtilities

and externally binding the utils model name to a package that has a CopyUtilities class with suitable a CopyOclExpession operation.

The whole Concrete Syntax section deserves a much more substantial description.

In particular...

The mechanism by which a package name is located is unresolved, perhaps deliberately,
but the omission should be explicit.

What constraints exist on forward referencing of names?

Transformations and mappings could be ordered so that forward references are avoided,
but large modules benefit from an alphabetical ordering of elements, so requiring
a parser friendly order is not user friendly.