Data, Processes, and Events: Keys to Comprehensive Analysis - High-Performance Web Databases: Design, Development, and Deployment - page 62

Exhibit 4-15. Data flow diagram enhanced with event symbols.

This type of diagram (see Exhibit 11)
effectively shows events and relates them to major data entities. However,
it does not show the relationships among data entities other than through
the perspective of events.

The Structured Event Network.

The coverage of the Data Flow Diagram can easily be expanded
by simply adding the event to the process legend, as shown in Exhibit 15. Var-
ious kinds of events can be illustrated in this manner. For example, the pro-
cess-to-process data flow shown between processes 1and 2 in Exhibit 15 illus-
trates a stage change triggered by a change in state in the same entity. In other
words, as the ELH in Exhibit 14 illustrates, as soon as an order is edited, it
goes immediately to the fulfillment stage. Because there is a data store
between processes 2 and 4 in Exhibit 15, the diagram implies that a waiting
time or delay exists. The legend in process 4 confirms that it is triggered every
two hours; process 2 is triggered by input that starts with process 1. Process
6 illustrates a stage change in one entity triggered by a stage change in
another entity; process 6 deletes the order and creates order history.

The DFD.

The EERD

Although the techniques discussed in the previous section enhance the
capabilities of the analysis tools discussed in this chapter, an event-driven