If A sends an async message to B like for example, to load async images to UI from the web. Where should the response message go?
Should it be slant as well or direct? And where would the activation of the sender (A) would be?
How to Represent Async Response in UML Sequence Diagram
sequence-diagramuml
Related Solutions
There are 2 things to consider, in general:
- The intended audience of your UML documentation
- How critical the algorithm is to the success of the project
Are you creating these diagrams as part of a design review for non-technical (or rather, non-software) customers? If yes, then do not bother including the algorithm. Its too low level, and you will lose the audience.
Will the diagrams be used as overall reference for maintenance programmers? Assuming there is nothing special, new, or technically innovative about this seek algorithm, then don't bother. Comments could be enough.
Alternatively, for some reason, it could be vital that the software perform this seek efficiently. Or reliably. Or the algorithm itself is special, new or technically innovative. In that case, document it in whatever form is appropriate - pseudo-code, UML sequence diagrams, etc. If it is important to the success of the project, then the diagram is likely to be referenced in the future.
One way is to use Fragments like this:
But honestly: code is much clearer for such purposes. Avoid using a graphical representation where a few lines of (pseudo) code can clarify what a 1000 pictures obfuscate. Once (in the 80s) I also though that programming graphically would be an advantage. But now I'm old an wise and know that this was wishful thinking. It's simply stupid ;-)
Regarding the IOException this heavily depends on runtime behavior. Usually this is a message sent from c which is not a return message but will produce a call stack in a. This can be placed in an alt Fragment.
Best Answer
There are two questions here: 1. The slanting of the arrow(s) and 2. what to do with the activation.
The arrows should be slanted if you want to represent in your diagram that it takes time for the message to travel from A to B or vice-versa.
If you just want to indicate that the message is processed a-synchronously, it is enough to use an open arrow-head on the message.
When a message (sent from A to B) is processed a-synchronously, then the activation of A ends as soon as the message has been sent and starts again when the response from B is received.
This is under the assumption that A does not block while waiting for the response, but it would be able to do some other processing while waiting for the response.