Behavior : Sequence Diagrams - Messages

5 important questions on Behavior : Sequence Diagrams - Messages

How do we draw messages?

They are normally horizontal arrows leaving the sending lifeline and arriving at the receiving lifeline

In Table 14.1, rows 1 through 4 show messages being sent and received.

What can be passed in messages?

Argument values can be passed in all these messages.

Be careful that the argument values match up with the formal parameter types where the message is defined.

The sender waits for a return.

How do we implement this?

Typically, we implement this by an operation call.

In Fig. 14.2, we have an exchange of synchronous messages.

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While the sender waits until getting the return, it does not mean that ....

the sender is necessarily blocked from sending or receiving other messages.

Nonblocking yet synchronous behavior is allowed in order to account for the possibility that the sender may have multiple parts or threads, and the waiting may block only one.

Because no reply is possible, an asynchronous message cannot have a ..?

return or output parameters.

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