There are three ideas to consider:
1.  Combined Fragments
This is the optional/alternative box that Scott recommended.  They are called combined fragments.  They look like a set of rectangles joined top to bottom, each rectangle representing a different alternative. This URL shows you what they look like: (scroll down to alternative combined fragment)
2.  Interaction Occurrence / Interaction Use
Now, if the messages in each fragment are a small set with few objects, you can include them right in the rectangle.  But if there are a lot of messages and plenty of objects, many of which are only used inside of the fragment, you may want to put them on a separate diagram.  To link the new diagram to the old, you will use an Interaction Occurrence.  The same URL above shows you an Interaction Use.
3.  Use a note
If the messages are a single message each, some people just plop a note down, anchor it to each message and say Alternate Flows.
Hope this helps!

From: [] On Behalf Of Scott Fleming
Sent: Tuesday, August 19, 2008 8:43 AM
Subject: Re: [uml] Condition in sequence diagram

UML  sequence diagrams offer the concepts of optional and alternative sequences. They are each represented by a box around a sequence. Alternative is sort of like if...elseif...else logic. Optional logic is sort of like if this condition is true then do this stuff with out the else condition.
Scott Fleming

On 8/19/08, uml <> wrote:
I have an actor which can click on for example save or cancel and I have a class which define my form how should I connect this actor to the class? How should I show that that actor has a choice between clicking on save or cancel button?(events in programming)

Best regards:

         Kianoosh Akhavan Karbassi

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