Author Topic: Can instances head lifelines in sequence diagrams?  (Read 2190 times)

qwerty

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Can instances head lifelines in sequence diagrams?
« on: November 08, 2015, 07:42:54 am »
I stumbled over this interesting question on LinkedIn: https://www.linkedin.com/grp/post/1330747-6068850012656250883

Now looking at EA there has always been some (confusing) mix of instances and lifelines. But if I interpret the current UML spec correctly lifelines and instances are different concepts. And thus instances must not appear in SDs.

Uffe

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Re: Can instances head lifelines in sequence diagr
« Reply #1 on: November 11, 2015, 12:29:30 am »
Well... The UML spec concerns itself more with visual representations than underlying data models, first off.

Looking at 9.8 (Instances) and 17.3 (Lifelines), it's clearly true to state that Lifelines and Instances are not precisely the same thing. But I wouldn't conclude that Lifelines should be Classifiers either.

Chapter 9 defines concepts used in classification -- Classifiers, Features, Operations, Instances, etc. These are all part of the "structural modeling" semantic area of UML.
Chapter 17 is about interactions -- Messages, Fragments, Lifelines, and so on. These are part of the "behavioral modeling" semantic area.

In other words, you can't read the two side by side -- it's comparing apples and oranges.

All that said, Annex D clearly lists Lifelines as having both an Instance and a Classifier (actually a Class, but Actors, Components etc are specializations of Class).

So I can't see anything wrong with EA's implementation of lifelines.


/Uffe
« Last Edit: November 11, 2015, 12:30:22 am by Uffe »
My theories are always correct, just apply them to the right reality.

qwerty

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Re: Can instances head lifelines in sequence diagr
« Reply #2 on: November 11, 2015, 12:59:41 am »
I did not say it's wrong but rather it's confusing. You can place lifelines a objects on a SD and the look the same - except for the browser where bote have different icons.

OTOH where I think that EA is wrong is that you can place a class on a SD and it behaves like a lifeline - until you first ex.-/import it via XMI.

q.

Simon M

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Re: Can instances head lifelines in sequence diagr
« Reply #3 on: November 11, 2015, 08:24:40 am »
Quote
OTOH where I think that EA is wrong is that you can place a class on a SD and it behaves like a lifeline - until you first ex.-/import it via XMI.
As I've had to say a few times recently off-forum... It's amazing how insistent users can be about using non-conformant behavior. We've long recommended against it. There was even a build where it was harder to directly drop classifiers as a lifeline. It had to be rolled back quickly.
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Glassboy

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Re: Can instances head lifelines in sequence diagr
« Reply #4 on: November 11, 2015, 09:18:53 am »
Quote
As I've had to say a few times recently off-forum... It's amazing how insistent users can be about using non-conformant behavior. We've long recommended against it. There was even a build where it was harder to directly drop classifiers as a lifeline. It had to be rolled back quickly.

Well I was asked to use a different UML tool but I resisted as one of the strengths of EA is I can misuse it when I need to :-)

qwerty

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Re: Can instances head lifelines in sequence diagr
« Reply #5 on: November 11, 2015, 09:59:09 am »
OMG ::)

q.