UML24 — UML 2.4: “Figure 7.31 shows the dot at the wrong end.”

UML 2.4: “Figure 7.31 shows the dot at the wrong end.” From: Pete Rivett pete.rivett@adaptive.com
Sent: 14 December 2010 17:50
To: Steve Cook
Cc: Maged Elaasar; andrew@omg.org
Subject: RE: New notation for attribute

No it did not come from me: I think it was Jim or Bran or Ed (see attached).

However attached is an updated figure I drew from scratch.

Pete

From: Steve Cook Steve.Cook@microsoft.com
Sent: Tuesday, December 14, 2010 4:44 AM
To: Pete Rivett
Cc: Maged Elaasar; Andrew Watson (andrew@omg.org)
Subject: RE: New notation for attribute

Pete – I believe you made that figure. Is it possible to supply a correct one?

From: Pete Rivett pete.rivett@adaptive.com
Sent: 13 December 2010 20:10
To: Ed Seidewitz; Steve Cook; Bran Selic
Cc: BERNARD, Yves; uml2-rtf@omg.org
Subject: RE: New notation for attribute

I agree the diagram should be fixed as an editorial change: things are confusing enough as it is. We need to check with Andrew on the correct procedure.

In terms of the concepts, it seems that navigability is the thing we should lose – specifically for metamodeling.

What does it mean to say that it’s not possible (‘efficiently’) to navigate from a class to its specializations (for example)? What modeling tool would disallow a user (or OCL conditions or QVT transformations) from discovering this information?

That’s not to say navigability has no value for other types of model. I don’t feel qualified to comment. Clearly some people like it.

However, given the current definition of navigability and the fact that we have the dot notation (love it or hate it) for end ownership, I propose we eliminate the use of navigability from the definition of UML itself (and indeed any other metamodel) – since it’s redundant, confusing and makes no sense for metamodels. And it sets a poor example for use of navigability as a general modeling capability.

This will make no difference at all to the XMI for model interchange – since it’s the end ownership that determines serialization. So I believe it is something we should do for UML 2.5.

Pete

From: Ed Seidewitz ed-s@modeldriven.com
Sent: Monday, December 13, 2010 10:21 AM
To: Steve Cook; Bran Selic
Cc: BERNARD, Yves; uml2-rtf@omg.org
Subject: RE: New notation for attribute

Steve –

I checked the actual resolution in Ballot 5, and the revised text actually does proposed updating the diagram with the dot in the wrong place. So the document was indeed updated properly per the resolution. However, the issue itself called for the use of the dot notation, which was simply applied incorrectly in the figure update. I am concerned that, now that the figure has been noticed, some people will start actually thinking that the “dot on the wrong end” is the right way to show an attribute using “association-like notation”, which will just cause even more confusion!

As to getting rid of the dot notation, the was a looong discussion in the UML 2.0 FTF about the need to have both the concepts of navigability and end ownership and that these need to be separated (which they were not in UML 2.0 as originally submitted). You can talk to Conrad Bock more about the reasons for this, but unless the constituency behind this has gone away (which I don’t think it has), I don’t think we will be able to get rid of the dot notation. In the past 5 years, no one has really like this notation, but no one has come up with anything better that satisfies everyone involved!

– Ed

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From: Steve Cook Steve.Cook@microsoft.com
Sent: Monday, December 13, 2010 1:09 PM
To: Ed Seidewitz; Bran Selic
Cc: BERNARD, Yves; uml2-rtf@omg.org
Subject: RE: New notation for attribute

I’ve said it before and I will say it again: the dot notation for association end ownership is a mistake. To put it mildly. No normal user of UML cares a fig about this stupid dot. It means nothing semantically, being purely about model management, and is a step in diametrically the wrong direction, simply adding more unnecessary complexity UML.

The fact that the RTF screwed it up in 2.4 only goes to show how non-intuitive this notation is: it gets through an RTF review and vote, despite the fact that the proposal is introduced by a UML expert and represents the simplest possible example.

I don’t believe that this is an editorial change. I think we deserve to be embarrassed by it for a good few months. Maybe this embarrassment would convince us to get rid of the thing altogether in 2.5.

– Steve

From: Ed Seidewitz ed-s@modeldriven.com
Sent: 13 December 2010 17:55
To: Bran Selic
Cc: BERNARD, Yves; uml2-rtf@omg.org
Subject: RE: New notation for attribute

Bran –

You are right, I was looking at the UML 2.3 spec. The resolution to Issue 10087 changed Figure 7.31 “to show dot-notation”. But it looks like the dot was placed at the wrong end! I am hoping this can be considered an editorial error that can be fixed in the final clean up of the spec document (Steve, Maged??).

In any case, I think the intention was that this notation alternative look exactly like association notation – that is, it is indeed overloaded notation, which I agree is a bad idea. But changing this would be more than an editorial change, hence the suggestion of recording this as an issue.

– Ed

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From: bran.selic@gmail.com bran.selic@gmail.com On Behalf Of Bran Selic
Sent: Monday, December 13, 2010 12:42 PM
To: Ed Seidewitz
Cc: BERNARD, Yves; uml2-rtf@omg.org
Subject: Re: New notation for attribute

???I believe that you are saying that this is a case of an overloaded notation. If I understood you correctly, you are telling me that the line that looks like an association is not an association and that the black dot – which definitely appears on one line end in Figure 7.31 in my copy of ptc/10-08-02 (smudge on my screen?) – which looks like the notation for denoting end ownership also means something else (and, furthermore, reverses the usual convention).

Ugh! Overloading notations is a bad idea.

Cheers...Bran

On Mon, Dec 13, 2010 at 12:31 PM, Ed Seidewitz <ed-s@modeldriven.com> wrote:

Bran –

I don’t see any black dot at all in Figure 7.31. Note that there are no association ends in Figure 7.31, since it is showing an attribute Window with no association. It just looks like an association, which is an ambiguity in the notation which should probably be fixed. Just putting a black dot on the far end would still leave the graphical notation ambiguous as to whether there was actually an association or not. Not having any association end name at the near end is not enough, since this can be suppressed even when there is an association.

– Ed

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From: bran.selic@gmail.com bran.selic@gmail.com On Behalf Of Bran Selic
Sent: Monday, December 13, 2010 12:14 PM
To: Steve Cook
Cc: Rouquette, Nicolas F (316A); BERNARD, Yves; uml2-rtf@omg.org

Subject: Re: New notation for attribute

Hmmmm. That example looks wrong to me; that is, the black dot is at the wrong end. I believe the intent of this example was to show an attribute Window::size[1] of type Area. But, according to Figure 7.19, the black dot indicating end ownership should appear on the association end that is AWAY from its owning classifier. But, the diagram in figure 7.31 has the black dot on the near association end. Do I have this wrong?

In retrospect, we should have simply completely dispensed with the concept of navigability and retained the arrow to mean end ownership, which is what most people expect and which is actually intuitive. The black dot is not intuitive and bound to create confusion – such as the case above (regardless of whether I am right or wrong above).

Cheers...Bran

On Sun, Dec 12, 2010 at 6:59 AM, Steve Cook <Steve.Cook@microsoft.com> wrote:

I believe this option is already there: see figure 7.31.

From: Rouquette, Nicolas F (316A) nicolas.f.rouquette@jpl.nasa.gov
Sent: 11 December 2010 11:59
To: BERNARD, Yves
Cc: uml2-rtf@omg.org
Subject: Re: New notation for attribute

Yves,

This idea makes sense as part of the Diagram Definition for UML.

• Nicolas.

On Dec 10, 2010, at 4:01 AM, BERNARD, Yves wrote:

According to several discussions I had with UML users, it appears that many of them, who have the intent to simply to add an attribute to a class, finally create an association to the type of the required attribute. In all case I faced, the reason was that they prefer the notation UML proposes for association which is much more powerful. Mainly:

Capability to get a modular diagram thanks to the “link notation”
Capability to show the aggregation kind

However attributes and association are not the same and it is a pity to introduce such a drift in the semantics just because of the notation.

What do you think about adding a notation for the attributes that would offer the capability to represent all their properties and to designate their type using a link?

Replace the offending diagrams.