CS2002 - Week 5 - Sequence Diagrams

Synchronous message

Sender waits until it has received a response message before continuing (close arrowhead)

Asynchronous message

Sender continues without waiting for a response message (open arrowhead)

Response message

May be omitted if content and location are obvious

alt

alternative interaction, similar to switch statement in java, conditional branches with guards

opt

optional interaction, similar to if statement without else branch

loop

repeated interaction

break

exception interaction, simple form of exception handling

seq

weak order, interactions occur in strict sequence order

strict

strict order, interactions occur in more restrictive order without parallelism or out-of-order execution, messages must follow vertical order

par

concurrent interaction, allows parallel interactions, messages can interleave

critical

atomic interaction, ensures interaction complete without interruption, messages can't interleave

ignore

irrelevant interaction, specifies messages that should be ignored and not shown in the diagram

consider

relevant interaction, specifies which should be considered while ignoring others

assert

asserted interaction, specifies an assertion that must always be true for sequence to proceed

neg

invalid interaction

Sequence diagram purpose

Shows interactions between objects in chronological order