Bidirectional arrows in sequence diagrams

[pink]

Hi,

Does anyone know how to get bidirectional arrows in sequence diagrams? I am sure it's there but I just can't see it.  

Thanks in advance!

[sargasso]

I must admit this is quite perplexing.

Given that a directed connection, i.e. a single headed arrow, is supposed to represent a message (signal or call) from an instance of one classifier to an instance of another, just what is a bi-directional arrow supposed to represent?

b

[«Midnight»]

Dialing your own number?

[sargasso]

I'm gonna get shot for this one but...

Two women talking?

Cheryl::lady  <--------> Beryl::lady
Cheryl::lady  <--------> Beryl::lady
Cheryl::lady  <--------> Beryl::lady
Cheryl::lady  <--------> Beryl::lady
...


OK. I'll go back to sleep now. (MODS: Please kill this quickly)
b

[Eve]

I don't think a bi-directional arrow makes sense on a sequence diagram.  It's certainly not available in EA. I tried thinking of what it might mean, something like a shorthand for call and return, but that makes it impossible to see what is calling what.  A more normal shorthand is not showing the return.

But the key question, is what are you trying to show.  Then maybe we can make a recommendation about how to show it.

(I'd be thinking asynchronous messages that cross for that kind of conversation.   :-/)

[pink]

okay..I am trying to show a message that could be sent by either node (like an error message) ..I guess I am trying to use seq diagrams for diagrms which are not really seq diagrams.

I could separate it out into two diagrams and show that the message could be sent by either node.

[Eve]

Given that a sequence diagram usually represents a single flow of events  (alt blocks excluded) I think it would be a good idea to split it up.