Operation contracts may be defined for
system operations operations that the system as a black box component offers in its public interface. System operations can be identified while sketching SSDs, as in Figure 11.2. To be more precise, the SSDs show
system events events or I/O messages relative to the system. Input system events imply the system has system operations to handle the events, just as an OO message (a kind of event or signal) is handled by an OO method (a kind of operation).
The entire set of system operations, across all use cases, defines the public
system interface , viewing the system as a single component or class. In the UML, the system as a whole can be represented as one object of a class named (for example)
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