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Re: [] Question regarding numeric types


I agree with the value semantics part. That's not a problem with EMF/Java semantics because Java collections don't compare by identity of the Java primitive wrappers but by equality. So the "this 3 != that 3" doesn't cause problems.

The OCL conformance of Integer to Real is really a pain in the neck from the Java perspective, probably the specification of the type Real as such: "The standard type Real represents the mathematical concept of real." I can always write an expression

	let r:Real=1.0/3.0 in r*3

and hope to get back 1.0. But how realistic is that in practice? Even one step further:

	let r:Real=1.0/3.0 in 1=r*3

How likely is it that all OCL implementations will solidly return true in this case? This seems a very unreliable operation except for writing is as documentation next to some model (which I care less about than I do care about executable specifications).

Also, from an EMF perspective, the int 3 == double 3.0 doesn't matter so much because I'm not aware of an EMF case where this type of comparison collapses the two values. All collections in Java are Object-typed, therefore will use the wrappers.

The potential inconsistency between an EMF x.many_feature.size() and a corresponding OCL x.many_feature->size() is pretty irritating.

-- Axel

On 4/18/2011 3:16 PM, Willink, Ed wrote:
Hi Axel

Interesting observation.

Pedantically, OCL 2.0, 2.2, 2.3 has no explicit numeric equality semantics.

=(object2 : OclAny) : Boolean
True if self is the same object as object2. Infix operator.
post: result = (self = object2)"

which does not require that this 3 is equal to that 3.


IMVHO OCL is primarily a specification language and so should be highly
implementation-independent; although I'm not convinced that million-digit
precision is totally necessary or practical for division.

OCL should support libraries so migration should be an issue.


OCL cannot just adopt Java semantics because Java has three different
semantics for two different equalities

value-semantics: int 3 == double 3.0
object-semantics: Integer 3 != Double 3.0, and this Integer 3 != that
Integer 3
object-value-semantics: Integer 3 !.equals Double 3.0, but this Integer 3
.equals that Integer 3


OCL does have Integer to Real conformance which strongly suggests that if

this Real 3 = that Real 3, then this Real = that Integer 3

I think that anything other than value-semantics for OCL numerics is almost


The EMF anomally is embarrassing, but can be worked around by ensuring
the the EMF UniqueEList is assessed for OCL uniqueness when creating a
corresponding SetValue. This should lead to no inconsistency, any access
within OCL should see the collapsed collection.

In order to be more EMF-friendly, the EMF OCL Standard Library which must
define the mapping of Etypes to OCL primitives can define its own variant

NB. With a modelled library, equality is defined by the library not by OCL.

[I haven't got the code to hand, but I suspect that SetValue is already
collapsing a collection, using polymorphic Value equality, which is
built-in. It's one of a number of areas that can be more model driven.]



-----Original Message-----
[] On Behalf Of Axel Uhl
Sent: 18 April 2011 13:09
To: MDT OCL mailing list
Subject: [] Question regarding numeric types

Ed, all,

I'm wondering how OCL semantics for numeric types interferes
with Java's
definition. We had this discussion before. But here's a
thought that I
think hasn't been brought forward yet.

If we integrate OCL with Ecore/EMF then on the EMF side there are
collection types and their constraints, derived from the Ecore
multiplicity settings. For example, there is UniqueEList. It's
add/contains is based on regular Java equality.

With this, an EObject many-feature that is modeled as unique
can easily
hold EDoubleObject and EIntegerObject values that are not equal
according to Java semantics but will be equal according to
standard OCL
semantics. If an OCL PropertyCallExp accesses such a feature, an
inconsistent OCL collection will result, inconsistent in one
of two ways:

   - if OCL chooses to collapse values equal to each other
according to
OCL semantics, the property's cardinality will differ from the EMF
feature's cardinality

   - if OCL leaves the values distinct according to Java semantics in
place, the collection is inconsistent from OCL's point of
view because
it should be unique but has two distinct values equal
according to OCL

  From an EMF/Ecore perspective, the most pragmatic way out of this
dilemma seems to be to alter OCL semantics such that they comply with
Java semantics. In particular, this would make 3.0<>  3 which
might come
as a shock to the OCL purist but would probably be fairly
intuitive to
Java/EMF/Ecore consumers.

The implications, of course, are horrible in another sense. OCL
expressions would not be entirely portable across
environments. But: is
this a dominant use case? What would it look like? How would I obtain
and re-use a significant body of OCL-implemented libraries in
a platform
context different from the one where it was developed?

-- Axel
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