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The following box describes the formal
rationale.
FIGURE 2-29
System interaction points for the on-board computer.
bdd [package] System context [interaction points]
CarControlPort
CarReaderPort
IOPort
ServerPort
ServicePort
KeyPort CurrentPort
MicrophonePort
CarPort
?«System?»
On-board computer
63
WHY ARE ASSOCIATIONS NOT PERMITTED ON PORTS?
It is often very enticing to connect an association with a port, e.g., in the system
context diagram or in the block definition diagram. Though this is in fact supported
by several SysML/UML tools, it is formally illegal. And a closer look reveals that it
doesn ??™ t make any sense. A port is a property of a block and has a rank similar to
that of an attribute. Attributes must not be connected with associations either.
The internal block diagram looks at more detailed structure aspects than the
block definition diagram. For example, you could model how the properties of a
block??”ports and attributes??”relate. You could then use a connector which, in
turn, can have an association as its type, to connect a port.


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