[mdt-ocl.dev] Numeric values as notional singletons

[Ed Willink <ed@xxxxxxxxxxxxx>]

Hi

I've just appended the attached to OMG Issue 14918.

Any opinions on whether

Set{ 3.oclAsType(UnlimitedNatural), 3.oclAsType(Integer), 3.oclAsType(Real) }->size() = 1.

Sequence{3, 3.0}->count(3.0) = 1.

is the interpretation that we want?

Certainly not quite what I would have expected, but anything else seems much worse.

    Ed

-------- Original Message --------

Subject:	Re: issue 14918 -- OCL 2.1 11.2.5 Numeric = and <> operations should compare values
Date:	Sat, 16 Jan 2010 12:48:33 +0000
From:	Ed Willink <ed@xxxxxxxxxxxxx>
To:	ocl2-rtf@xxxxxxx

Hi

The problem of value object identity is much more widespread.

All the collection operations such as count(), includes() etc are based on objects, so it is unclear whether

Set{ 3.oclAsType(UnlimitedNatural), 3.oclAsType(Integer), 3.oclAsType(Real) }->size() is 1, 2 or 3.

and whether

Sequence{3, 3.0}->count(3.0) is 1 or 2.

For 3.oclAsType(UnlimitedNatural) and 3.oclAsType(Integer) to be different 'objects' would be very confusing,
so 3.oclAsType(Integer) and 3.oclAsType(Real) must be the same 'object' too.

It is presumably sufficient to specify that each distinct numeric value is notionally represented by a singleton value object of the narrowest possible PrimitiveType. Thus 3 and 3.0 are both represented by the 3.oclAsType(UnlimitedNatural) singleton. Implementations may use multiple non-singleton value objects, but these may not be observably distinct.

Therefore:

Set{ 3.oclAsType(UnlimitedNatural), 3.oclAsType(Integer), 3.oclAsType(Real) }->size() = 1.

Sequence{3, 3.0}->count(3.0) = 1.

    Regards

        Ed Willink

On 06/01/2010 21:44, Juergen Boldt wrote:

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Date: Sat, 02 Jan 2010 18:56:24 +0000
From: Ed Willink <ed@xxxxxxxxxxxxx>
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To: issues@xxxxxxx
Subject: OCL 2.1 11.2.5 Numeric = and <> operations should compare values
 rather than objects
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Hi

OCLAny::=() is defined as 'True if self is the same object as object2.'

This is not overloaded for numeric types, and it is not specified that a numeric value may not have multiple instances.

The definition therefore implies that:

1 = 1

may often evaluate to false, and that

1.0 = 1

must evaluate to false even though (1.0 <= 1) and (1.0 >= 1) will evaluate true

Suggest overload {Boolean, Real, String}::{=,<>} to use values rather than objects.

    Regards

        Ed Willink

Juergen Boldt
Director, Member Services
Object Management Group
140 Kendrick St
Building A Suite 300
Needham, MA 02494
USA

tel: +1 781 444 0404 x 132
fax: +1 781 444 0320
email: juergen@xxxxxxx
www.omg.org