Guideline: Identify Service Interfaces from Collaboration Role Interaction Patterns presents four rules for describing ServiceInterfaces based upon pairs of interacting roles in Service
Collaborations. The rule illustrated here is:
Rule 4. Create a ServiceInterface with a provided interface and a required interface when the provider
role responds back to the consumer role with a callBack message. In this case,
the provider role requires that the user be able to accept messages; therefore, the provider requires an interface
with the consumer.
In Figure 1, "role1" sends a message to "role2," and "role2" responds with a callBack. From the perspective of
the provider, "role2," two interfaces are involved:
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A provided (realized) interface that offers the operation: "do This"
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A consumed (required) interface that offers the operation: "callBack"
The ServiceInterface might be created and configured as shown in Figure 2.
Figure 1. The callback collaboration pattern
Figure 2. Modeling the structure of a complex service interface
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