Author Topic: What is a "property"?  (Read 5823 times)

Boron

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What is a "property"?
« on: July 31, 2017, 11:42:24 pm »
Hello,

since several weeks I am asking myself the hell is a "property" when dropping a class element in a diagram.
When dropping a class element in a diagram a dialog appears asking of what kind the dropped element shall be created: Link, Instance, Child, Property.

Links, Instance and Child are perfectly clear.
I just don't know what a property might be.

Can anyone bring light into my darkness?
All explanations in the internet did not really help (maybe bad explained or I am too stupid for that).

PeterHeintz

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Re: What is a "property"?
« Reply #1 on: August 01, 2017, 01:10:28 am »
In addition to attributes, there are some UML Class based languages having properties as well.
One example is SysML Block diagrams were a Block (more or less a Class) can have many specific kinds of properties.
Properties are similar to attributes but not the same.
Best regards,

Peter Heintz

Paolo F Cantoni

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Re: What is a "property"?
« Reply #2 on: August 01, 2017, 10:19:25 am »
The term "property" has many meanings, depending on both the domain and/or the context of usage.  It's unfortunate, but there it is.

In addition, its meaning can vary depending on whether one is speaking in narrative or technical terms.

Paolo
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KP

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Re: What is a "property"?
« Reply #3 on: August 01, 2017, 10:37:33 am »
When dropping a class element in a diagram a dialog appears asking of what kind the dropped element shall be created: Link, Instance, Child, Property.

Paolo is correct that Property has many meanings depending on context. In this context, it is used as a synonym for Part.
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Paolo F Cantoni

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Re: What is a "property"?
« Reply #4 on: August 01, 2017, 12:11:29 pm »
When dropping a class element in a diagram a dialog appears asking of what kind the dropped element shall be created: Link, Instance, Child, Property.

Paolo is correct that Property has many meanings depending on context. In this context, it is used as a synonym for Part.
Only Part?  If so, why not just use Part?  Why use a synonym (whose meaning is often not identical with the original term) when there is a perfectly acceptable (and, in this case, absolutely accurate)  term already available?

Now that I've got involved with OntoTerminological Modelling, it has helped me work out some of the background rules or guidelines to enable as clear communication as possible.  As a consequence, I've had to modify some of my language usage - hopefully for the better.  :)

Paolo
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PeterHeintz

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Re: What is a "property"?
« Reply #5 on: August 01, 2017, 04:29:55 pm »
Well, at least in SysML a property might be a part but it might be a shared thing as well or a Feature or a Flow Property, or ...
Best regards,

Peter Heintz

Paolo F Cantoni

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Re: What is a "property"?
« Reply #6 on: August 01, 2017, 04:55:25 pm »
Well, at least in SysML a property might be a part but it might be a shared thing as well or a Feature or a Flow Property, or ...
Granted, Peter,

But in the context of dragging (and dropping) a class element onto a diagram (as Boron originally mentioned)...

Paolo
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Richard Freggi

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Re: What is a "property"?
« Reply #7 on: August 02, 2017, 12:17:00 am »
In UML 2.5 a property is just a catch-all name for a feature of a classifier.  The excellent (and concise) "The Unified Modeling Language Reference Manual, second edition" by Rumbaugh, Jacobson and Book takes 7 PAGES to explain properties.  So, I suggest you just roll with it.....

PeterHeintz

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Re: What is a "property"?
« Reply #8 on: August 02, 2017, 01:03:32 am »
Hello Paolo,
yes, you are right.
The term property has just too many meanings depending on the context it is used.
Maybe “Role/Reference” instead of “Property” would fit better to that dialog.
Best regards,

Peter Heintz

Simon M

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Re: What is a "property"?
« Reply #9 on: August 02, 2017, 08:56:07 am »
The dialog is just using the UML term for what is created. In that sense, it's the easiest term to use.

Reference/Part and part both have specific meanings in SysML, while Property is the catch all term that encapsulates all usages.
Simon

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PeterHeintz

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Re: What is a "property"?
« Reply #10 on: August 02, 2017, 09:20:58 pm »
According UML spec. 9-5.1
Properties are StructuralFeatures that represent the attributes of Classifiers, the memberEnds of Associations, and the parts of StructuredClassifiers.

So the dialog uses a superset term of what is happening.
The terms role and reference are used in both UML and SysML spec.

Now after looking in the UML spec. I think the best term to use would be “Aggregation”

But anyhow, I worked with the term “Property” for years and I can life with that in the future as well.
Best regards,

Peter Heintz

sargasso

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Re: What is a "property"?
« Reply #11 on: August 03, 2017, 12:16:28 am »
A classifier is a classifier.
An attribute/property/pin/part/pineapple/frangipani is an informational feature of the classifier.
It is "convenient", within a context to give such feature a "prominent" name.
There are 10 types of things about a classifier: attributes (informational features) and behaviors (things you can tell an instance to perform).
There are no other things.
No matter how you dress up reality with this, that or the other "approach" to modelling the universe.

A model is a picture of the universe that helps explain an aspect of something in the universe.
A house plan helps explain the dream between the architect and the builder.
A color patch helps (occasionally to) explain what the wall will look like when it is painted.

A UML diagram should be constructed to explain, within some conversational context, some aspect of a system.
If the so called "rules" of UML don't let me do that, then I break them.

Let me say this only once (for the second time)! The model is not reality. The house plan is not the house, the color patch is not the paint. To paraphrase(?) Sylvia Plath "A rose is a rose", a picture of a rose is not a rose but it may give some audience an idea of the plant that I am talking about.
Go think about a painting that you like, of a rose if you like, or a fish or a tree or a car or a scream. Why is it good? Because it engenders something in your psyche - it just "gels".

And explains.

Now consider the person who painted it. Were they worried about whether this shade of blue was called "Prussian" or "Cobalt"?
Or were they just using that shade to convey, as clearly as possible, to the "audience" some aspect about that flower that they wanted to explain?

Model to explain, perhaps even unto yourself, aspects of the universe. Dressing up models with OMG names and trying to comply with the so called "rules" is a waste of both your and your intended audience's waste of time.
Is a property the same as a "Prussian Blue"? I think not.

Not clear enough? Well let's go sit in a coffee shop tomorrow and you can explain to me "how to get from here to Tiffany's in time for breakfast", on the back of a napkin.  Would I expect a Google map of the world? (Complying to dog knows whatever "standard" they use.) Now, given the current context, that we are sitting in a cafe in rural South Australia - would you try and draw a google map?

Classifier: Location
Attribute: geopos? (whatever)
Behaviour: Describe_route(destination::Location) as Scribble_on_napkin

bah! Sometimes I think UML modelling has got to the point of acute cranial-recto-insertion.

b

p.s. This rave was in part incited by a recent post on the dreaded "more than one instance of the same entity on one diagram" dinosaur. In particular let me refer to figure 15.1 in the most recent adopted specification. Oh dear! There is more than one instance of an Adapter Behavior in that diagram. Oh dear, worlds will collide!  Oh no, don't tell me OMG just broke one of their own rules. Oh hang on - there is no such rule anyway. But why didn't they draw it with so many damn criss-cross lines as to make it totally unintelligible?

(Damn. It was another diagram, but the point is still there.)
« Last Edit: August 03, 2017, 12:38:38 am by sargasso »
"It is not so expressed, but what of that?
'Twere good you do so much for charity."

Oh I forgot, we aren't doing him are we.

qwerty

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Re: What is a "property"?
« Reply #12 on: August 03, 2017, 12:26:50 am »
Figure 15.1 on p. 372 of formal/2015-03-01 seems absolutely legit.

q.

sargasso

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Re: What is a "property"?
« Reply #13 on: August 03, 2017, 12:46:21 am »
? Same page (372), "Behavior" at top center and bottom left.
? And now I look at the there are two "Redefinable Elements" as well.
« Last Edit: August 03, 2017, 12:49:55 am by sargasso »
"It is not so expressed, but what of that?
'Twere good you do so much for charity."

Oh I forgot, we aren't doing him are we.

qwerty

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Re: What is a "property"?
« Reply #14 on: August 03, 2017, 01:34:23 am »
My brain...

However, I'd accept that as "kind of legit". EA has this nice italic display of generalized elements which has not found it's way into the UML specs.

q.