Figure 3.19 represents the interface CarKey with a receive signal, Key(removed:
Boolean) . The interface is implemented by the class On-board computer control .
This relation is described by the realization in Figure 3.20 . The arrow is denoted
similarly to a generalization, but with a dashed line.
Together with the realization, the class is obligated to realize the properties
of the interface. The interface is a contract that is fulfi lled by the realizing class.
Accordingly, the interface ??™ s receive signal shows up once more in the implementing
class. The class KeyDeposit is a user of the interface.
Alternatively the realized (offered) interface is denoted as a ball , while a used
(requested) interface is denoted as a socket . 9
The realization also comes as a more general concept in the same notation.
In that case, what is being realized doesn ??™ t have to be an interface; it can be any
specifi cation element. SysML uses this for the ?«satisfy?» relationship.
Interfaces are very common in software development, while SysML uses them
only for the specifi cation of standard ports.
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