IBM SG24-7368-00 manual Black-box sequence diagram

In Figure 4-2the operation reject trade, from a black-box perspective, would encompass the Enterprise Application’s request of the Quality Officer to update trade status, as well as Enterprise Application’s request of the Quality Engineer to update trade status.

Note that some operations consist of only one black-box interaction, the one that invokes that operation. This is the case with Provide Energy or AS Trade Details in the same diagram.

Figure 4-2 Black-box sequence diagram

It helps to keep this black-box sequence in mind as we proceed to the work of creating the white-box expansion of the operation. To create this expansion, first we will write an operation specification for each operation. This operation specification, like a use case specification, describes a sequence of events to accomplish a goal. To write one for an operation, we work our way through the black-box description of the operation, and elaborate the black-box actions into white box, by explaining how the elements at the next decomposition level collaborate to accomplish the operation.

In the accompanying example, we show how the operation initiate new sale is realized by a collaboration of the point of sale and order processing elements (here called subsystems).

Chapter 4. White-box thinking: Understanding collaboration 73