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71 ).
Bars can be used on the lifeline to show the positions at which the instance
belonging to the lifeline is active (i.e., where it executes behavior) ( Figure 3.71 ).
The bar represents a so-called execution focus . This notation is optional. Active
areas result automatically from incoming and outgoing messages.
3.8.3 Message
FIGURE 3-71
Creating an object in an interaction.
sd Unregister customer
:On-board computer
control
identifyCustomer(data)
new()
user:Customer
Defi nition
A message is a communication between two lifelines. It can be synchronous
or asynchronous, and it can invoke an operation, transport a signal, or create an
object.
Parts of the system send messages to each other to exchange information and
jointly execute a behavior. In the sense of UML and particularly of SysML, this is
not to be understood as mere operation calls in the context of a programming language.
For example, if you model a pumping system that pumps a liquid from A to
B , then this transmission can be seen as a message between A and B (send signal).


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