Issue 15272: MOF 2.0 9.1 Confusing instance superclass statement (mof2core-rtf)
Source: Model Driven Solutions (Dr. Edward Willink, ed(at)willink.me.uk)
Nature: Uncategorized Issue
Severity: 
Summary: The statement in clause 9.1 semantics


"Class Element is the superclass of all model elements in MOF, and is the
superclass of all instances of MOF model elements."


is confusing since instances do not normally have superclasses.


The statement could be interpreted to mean that every class always has
Element as a superclass including user-defined classes. But this would then
make it impossible to model lightweight application classes supporting
solely the required functionality.


Surely it is every M2 (and M3 and ...) class that has Element as a
superclass?


At M1 the superclasses are as modelled by the user.


This is significant for OCL since OCL inserts at least OclAny as the top
type at M1 in order to support some reflective behaviour. If Element really
is an M1 superclass, then OCL should align. If Element is not an M1
superclass, OCL should provide its reflection in OclAny. 

Resolution: closed no change
Revised Text: 
Actions taken:
June 2, 2010: received issue
April 6, 2015: closed issue
Discussion: 
The offending sentence is no longer in the specification document, the current text
describes the role of Element much clearer.
The concerns expressed by the issue author are possibly no longer current. Since
version 2.4, MOF and UML share a common metamodel, in which Element is on top
of the hierarchy for both. The only difference is, that MOF::Reflection::Element adds reflection capability to Element via extra operations and a derived association to the
Element’s metaclass.
End of Annotations:=====

m: "Willink, Ed" <Ed.Willink@thalesgroup.com>
To: "'issues@omg.org'" <issues@omg.org>
Subject: MOF 2.0 9.1 Confusing instance superclass statement
Date: Wed, 2 Jun 2010 11:03:13 +0100 
X-Mailer: Internet Mail Service (5.5.2657.72)


Hi


The statement in clause 9.1 semantics


"Class Element is the superclass of all model elements in MOF, and is the
superclass of all instances of MOF model elements."


is confusing since instances do not normally have superclasses.


The statement could be interpreted to mean that every class always has
Element as a superclass including user-defined classes. But this would then
make it impossible to model lightweight application classes supporting
solely the required functionality.


Surely it is every M2 (and M3 and ...) class that has Element as a
superclass?


At M1 the superclasses are as modelled by the user.


This is significant for OCL since OCL inserts at least OclAny as the top
type at M1 in order to support some reflective behaviour. If Element really
is an M1 superclass, then OCL should align. If Element is not an M1
superclass, OCL should provide its reflection in OclAny. 


        Regards
                        
                Ed Willink


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