But you could also think of some property that the enclosing context keeps once the user logs in. You could imagine that :PostPage knows it since it was specially created for the user interaction. But not here, since no such message is received.

the result of a response message previously received by the sending lifeline.

But not here, since the only message was votePost(vote)

a parameter of a message previously received by the sending lifeline.

an object visible by the sending lifeline, such as property of the enclosing context or a globally known object.

But not here, since your lifelines are anonymous (no symbol before the :)

an object corresponding to another lifeline.

The parameter symbols such as user in the message arguments can for example be: If deemed useful, this is a portion of a class diagram showing the relevant entities : Is it a correct approach, or should a third control object (called AuthenticationControl) be involved in order to get the current user? Where does the user argument come from?Ĭurrently I did it so that the boundary object PostPage calls votePost(user,post,vote), assuming that it has knowledge of the user entity associated to the actor participating in the use case. In the sequence diagram with the analysis objects for this use cases, there is a message votePost(user, post, vote).

4: the system throws a visual feedback to indicate that the operation has been performed successfully.

If the post was already voted by the user, the system will override the old vote with the new one. 3: the system registers the vote cast by the user.2: the user clicks the dedicated button, according to the vote he intends to cast that can be either a negative or positive vote.1: the user reaches the posts ( includes 'View Post' use case).Postcondition: the post is voted by the user

Precondition: the user must be logged and the post the user wants to vote exists I'm drawing some sequence diagrams to give a graphical depiction of the use cases written during the requirements elicitation phase for my project.

Message sequence diagram online