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Re: [mdt-ocl.dev] Question regarding numeric types
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Hi Axel
Interesting observation.
Pedantically, OCL 2.0, 2.2, 2.3 has no explicit numeric equality semantics.
Just:
"OCLAny
=(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
untenable.
----------------------------------------------------------------------
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
anyway
define the mapping of Etypes to OCL primitives can define its own variant
equality
semantics.
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
currently
built-in. It's one of a number of areas that can be more model driven.]
Regards
Ed
> -----Original Message-----
> From: mdt-ocl.dev-bounces@xxxxxxxxxxx
> [mailto:mdt-ocl.dev-bounces@xxxxxxxxxxx] On Behalf Of Axel Uhl
> Sent: 18 April 2011 13:09
> To: MDT OCL mailing list
> Subject: [mdt-ocl.dev] 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
> semantics.
>
> 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?
>
> Best,
> -- Axel
> _______________________________________________
> mdt-ocl.dev mailing list
> mdt-ocl.dev@xxxxxxxxxxx
> https://dev.eclipse.org/mailman/listinfo/mdt-ocl.dev
>
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