Re: sequence diagram for observer pattern
- From: Robert Martin <unclebob@xxxxxxxxxxxxxxxx>
- Date: Sun, 28 May 2006 11:39:46 -0500
On 2006-05-28 02:03:54 -0500, chandra.somesh@xxxxxxxxx said:
hi
i have been trying to design sequence diagram for the Observer patterns
but have hit a road block....given below is the brief description...
Given below is a single Subject and three observers (for example
sake)...the Subject is responsible for invoking the notify on it self
whenevr its state changes...and then it sends the update() message to
all its observers....
Subject ObserverA ObserverB ObserverC
|--------l
|<------l notify()
|
| update() |
|------------------------->| |
| update() |
|---------------------------------------------------->|
|
| update()
|-------------------------------------------------------------------------->|
Now this sequence diagram is constrainted in a way that..after a
notify..we have subject sending update to ObserverA and then to
ObserverB and then to ObserverC......
I can show the other variants such as A,C,B and B,C,A and B,A,C and
C,A,B and C,B,A and wrap each of them inside an "alt" block .
However this approach will lead to an explosion of "operands" in case
we have more Observers...so i would like to know how better could i
represent the observer patterns SD with all the possible order of
update() messages taken care of ??
Is there some way that UML 2.0 can represent this behavior ??
0..*
|Subject|------>|Observer|
| |
| 1:Notify |
+-----+ |
| | |
|<----+ |
| |
| 1.1*: Update |
|-------------->|
| |
If you must represent such things, you can do it as in the above. Note that the association between Subject and Observer is shown with a cardinality of 0..* and that there is a * in the sequence number of Update showing that the message repeats. No order is implied, and therefore all orders are valid.
However, I question why you must represent something like this. Drawing pictures of observers is almost certainly a waste of effort unless you have some very particular reason for doing so.
----
Robert C. Martin (Uncle Bob) | email: unclebob@xxxxxxxxxxxxxxxx
Object Mentor Inc. | blog: www.butunclebob.com
The Agile Transition Experts | web: www.objectmentor.com
800-338-6716 |
.
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- From: chandra . somesh
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