2.4 SequenceAlly Diagram

2.4 Sequence“Ally Diagram

FADs and TADs are good for getting a high-level view of fortress relationships. They do not go into detail about the sequence of events that link fortresses as a treaty unfolds. To see better how the allied fortresses coordinate their workflow to fulfill the overall treaty requirements, we use a sequence“ally diagram ( SAD ).

SADs are adaptations of the UML construct called class sequence diagrams. A SAD gives an overview of a single treaty. In a SAD, the heading of the card gives the name of the treaty. Within the treaty, each ally fortress is represented by a vertical line. Interactions between the fortresses are shown with one of three arrows, following conventions similar to those used in UML's class sequence diagrams. Full solid arrowheads show use of a synchronous drawbridge. Full hollow arrowheads show a synchronous drawbridge returning information. Half solid arrowheads show use of an asynchronous drawbridge. Underneath each arrow is the name of the gate.

Figure 2.4 shows a prototype of a SAD; Figure 2.5, an example. For now, don't worry about the details of synchronicity versus asynchronicity. I will cover that distinction in detail in coming chapters.

Figure 2.4. Prototype of a SAD

Figure 2.5. A Sample SAD