We will differentiate port types later on in the system design, as
described in Section 2.7.3.
A system port describes a point in the system that is used to exchange information
with actors. Such a port can be a virtual, conceptual point or an object
existing in the real world.
Now, how do we fi nd the ports in our on-board computer? We look at our system
context model and try to fi nd out what interaction point each single actor may
have to the system. There may be more than one. It could also be that the communication
of an actor with the system does not fl ow over a port. For example,
we won ??™ t model a port for the environmental effect temperature . In this case, the
exchange doesn ??™ t occur over a designated point.
It is not a good idea in this early project phase to anticipate design or implementation
decisions, or only to a very little extent. Use conceptual names for your
ports, such as ServerPort for SMS communication with the SpeedyCar server in
our system example. You can see our result in Figure 2.29 .
You cannot connect actors directly with ports even if it may look enticing and
useful from the graphical perspective.
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