UML – Handling Alternative Frames in Sequence Diagrams

sequence-diagramuml

Question

When an alt frame is used in a sequence diagram, and one of the two possibility end the sequence, how is "legal" to continue?

example

I need to represent a sequence in wich there are user and atm

the user insert card
the atm verify card
if card is valid, then it confirm card to user and the sequence continue
if not it to user and the sequence Stop

can someone represent this simple example?

I made this sequence:

Is correct?

I assume that the part follow the alt frame imply that "good" case is verified?

Or I need to put all of the sequence of "good case" in the "good case alternative section"?

how can I handle this situation?

Thank's in advance!

Best Answer

I assume that the part follow the alt frame imply that "good" case is verified?

No, that assumption is incorrect. The part following the alt frame will be done when either part of the alt frame completes.

Or I need to put all of the sequence of "good case" in the "good case alternative section"?

Yes, all the steps that belong to the "valid card" alternative of the alt frame need to be shown within that portion of the frame.
If that clutters your diagram too much, you can also draw a seq frame inside the alt frame. The seq frame contains the name of another sequence diagram that describes the steps happening at that point.

Another option is to use a break frame. That would contain the steps for an invalid card (with a guard condition). Either the content of the break frame is executed, or the part of the sequence diagram below the frame.

Related Solutions

How to handle long method names in sequence diagram

Aside:
Contrary to popular belief, long names are not always a bad thing. Used in moderation, they can be helpful. For example, if a method returns a boolean value that indicates that the application startup should be aborted if the execution fails while the application is starting up then one of these is more clear than the other:

getTerminateDuringStartup
getHaltApplicationStartupIfExecutionFailsDuringStartupFlag

On to the Question:
If the names are too long to conveniently fit in a diagram, consider creating short names in the diagram only and map them to the full method name.

For example: Use createPFCIDbbbbc in the diagram and include a page that maps the short name to the long name. Consider flagging the short names; one way is to add an asterisk to the front of shortened names. In that case, *createPFCIDbbbbc would indicate that it is a shortened name and createBlammyQ would indicate that it is not a shortened names.

On the map page, start with a statement like "Some method names are too long to conveniently fit in the diagrams that follow. In these cases the method name will start with an asterisk to indicate that it is a shortened name. The list below maps between the shortened names and the actual method name in code". Then have a simple table like this:

Shortened Name         Actual Method Name
createPFCIDbbbbc       createPathForCustomerIDblablablabla_click

UML – How to Show Retry in Sequence Diagram

One way is to use Fragments like this:

enter image description here

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.