To illustrate how DFDs are used to model the logic of data flows in information systems, we will present and work through an example.
Consider Hoosier Burger, a fictional restaurant in Bloomington, Indiana, owned by Bob and Thelma Mellankamp. Some are convinced that its hamburgers are the best in Bloomington, maybe even in Southern Indiana. Many people, especially Indiana University students and faculty, frequently eat at Hoosier Burger. The restaurant uses an information system that takes customer orders, sends the orders to the kitchen, monitors goods sold and inventory, and generates reports for management. [pic]
The information system is depicted as a data flow diagram in Figure 7-4. • The highest-level view of this system, shown in the figure, is called a context diagram. o This context diagram contains only one process, no data stores, four data flows, and three sources/sinks. o The single PROCESS, labeled 0, represents the entire system; all context diagrams have only one process, labeled 0. o The SOURCES/SINKS represent the environmental boundaries of the system. o Because the DATA STORES of the system are conceptually inside the one PROCESS, DATA STORES do not appear on a context diagram.
The analyst must determine which processes are represented by the single process in the context diagram. [pic]
As you can see in Figure 7-5, we have identified FOUR separate PROCESSES. • The main PROCESSES represent the major functions of the system, and these major functions correspond to actions such as the following:
1. Capturing data from different sources (e.g., Process 1.0) 2. Maintaining data stores (e.g., Process 2.0 and 3.0)
3. Producing and distributing data to different sinks (e.g., Process 4.0) 4. High-level description of data transformation operations (e.g., Process 1.0)
• These major functions often correspond to the activities on...