Chapter 5

Question--Explain the relationship between a DFD context diagram and the DFD level 0 diagram.

A context level diagram is a high-level view of the entire system represented as one process symbol. Data flows going into and out of the system and the external entities that interact with the system are the only other element of the system shown on this type of diagram. A level 0 diagram is the first view of the internal processes of the business system. These processes are shown from fairly high level, with subsequent diagrams depicting increasing levels of detail. The level 0 diagram shows the same data flows and entities as the context, as well as data stores associated with the system.

Question--Explain the process of balancing a set of DFDs.

Balancing involves assuring that all the information from a higher-level diagram is appropriately represented on the next level, or 'child' diagram. The child diagram shows more detail, but must show all the inflows and outflows to and from the parent process on the higher level diagram

Question--Suppose a process on a DFD is numbered 4.3.2. What level diagram contains this process? What is the process's parent process?

Level 2 diagram contains the process numbered 4.3.2 Parent process is 4.3

Question--Distinguish between logical process models and physical process models

Logical process models describe processes without suggesting how they are constructed. Physical process models provide information that is needed to ultimately build the system.

Question--Why is a process model typically composed of a set of DFDs? What is meant by decomposition of a business process?

Most business processes are too complex to depict using one diagram. Consequently, business processes are typically depicted with a set of DFDs, with the first diagram (Context Level) showing a summary of the system, and subsequent DFDs showing processes within that system. Decomposition is a method for breaking down a business process into smaller, logical processes.

Question--What is a process model? What is a data flow diagram (DFD)? Are the two related? If so, how?

Process models are used to document and organize the information obtained during the analysis phase of a systems development project. Data flow diagramming is a popular technique that is used in process modeling today. Data flow diagrams document the business processes and the data that passes among them.

Question--.Explain the use of structured English in process descriptions

Structured English is one method of describing a process. Typically, short sentences are used to describe the elements or steps in the process.

Question--Explain the relationship between a DFD level 0 diagram and a DFD level 1 diagram(s).

The DFD level 0 diagram depicts only the major high-level processes in the system. Each process is then decomposed into a more detailed DFD level 1 diagram. Typically a set of DFD diagrams for a system will include at least one DFD level 1 diagram for each process shown on the context level diagram.

Question--Discuss how the analyst knows how to stop decomposing the process model into more and more levels of detail.

The complexity of an overall system or business process that is being modeled sets the boundary conditions for knowing what is the "ideal" level of decomposition for any specific system or process. Processes are typically decomposed into lower-level DFDs when the additional decomposition helps to explain the complexity of the process; experts suggest that each DFD page have at least three, but not more than seven to nine, processes. A good rule of thumb is to consider a process decomposition complete when the process in question can be explained on one sheet of paper (e.g., structured English, Pseudocode), or with one process description model (decision table/tree