IBM SG24-7368-00 manual Operation analysis

Figure 4-1 Level 1 context diagram showing both human and non-human actors

Operation analysis

For each operation, the question we next need to answer is, how is this operation accomplished (or realized) as a collaboration of elements at the next level of decomposition? To answer this, we first write out the flow of events for the operation. Normally, when we write a flow of events, say for a use case, we keep to a black-box perspective exclusively. To realize an operation as a collaboration of lower level elements, clearly we need both black- and white-box perspectives.

In a way, we already have the black-box perspective of each operation. Look at the black-box sequence diagram of any use case that uses this operation. You will see a series of messages (requests) beginning with the one that invokes the operation. Follow this series of messages until you hit the next operation on the same element, or the end of the use case, whichever comes first and stop. What you have traced is the set of black-box interactions that accomplish this operation.

72Model Driven Systems Development with Rational Products