How I draw a try-catch in a sequence diagram
There is no standard way to model exception handling in a sequence diagram. However, exception handling is often critical. Here is how I visualise it. Remember, you can take quite some freedom in using UML. It is a language and as such it changes in lifetime. As long as your reader gets the idea you want to express, everything is perfect.
The above diagram is generated with
Web Sequencea free (open source) chrome extension. You can get it from here: http://bit.ly/web-sequence-ws or from the official site: http://bit.ly/zenuml.
To test it out, you can simply paste the following code into the code editor of the above plugin or on the site.
It demonstrates that we have a
try block. Within this block, we execute
Action.Execute() in which
InternalException could be thrown. Then we catch it, log an error and rethrow a
HighLevelException, which is a quite typical exception handling strategy.