Skip to main content

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [List Home]
Re: [] Question regarding numeric types

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-----
> From: 
> [] 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 
> 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
> _______________________________________________
> mailing list

Please consider the environment before printing a hard copy of this 
The information contained in this e-mail is confidential. It is intended 
only for the stated addressee(s) and access to it by any other person is 
unauthorised. If you are not an addressee, you must not disclose, copy, 
circulate or in any other way use or rely on the information contained in 
this e-mail. Such unauthorised use may be unlawful. If you have received 
this e-mail in error, please inform us immediately on +44 (0)118 986 8601 
and delete it and all copies from your system. 
Thales Research and Technology (UK) Limited. A company registered in 
England and Wales. Registered Office: 2 Dashwood Lang Road, The Bourne 
Business Park, Addlestone, Weybridge, Surrey KT15 2NX. Registered Number: 
Thales UK Limited. A company registered in England and Wales. Registered 
Office: 2 Dashwood Lang Road, The Bourne Business Park, Addlestone, 
Weybridge, Surrey KT15 2NX. Registered Number: 868273 

Back to the top