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Both the transmission of a signal and the call of an operation are represented
by a message. The notation is an arrow from the sender ??™ s lifeline to the receiver ??™ s
lifeline. Different arrow shapes mark different characteristics of a message.
Figure 3.71 describes a message to create objects. The arrow is dashed. For all
other forms of messages the arrow is solid, but with different arrowheads.
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A synchronous message has a fi lled arrowhead ( Figure 3.72 ). Synchronous
means that the sender waits until the receiver has processed the message. The
end (i.e., the return to the sender) is denoted by a dashed arrow.
An asynchronous message has an open arrowhead ( Figure 3.73 ). Asynchronous
means that the sender does not wait for the receiver; it can continue its own processing
work immediately upon sending the message. This implies that the sender
and the receiver are in different execution processes. There is no dashed return
arrow here.
3.8.4 Combined Fragment
3.8 Interaction Diagrams
FIGURE 3.73
Example for an asynchronous message.


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