| |SOLUTIONS FOR | | |CHAPTER 4 |
"Data flow diagrams and flowcharts provide redundant pictures of an information system. We don't need both." Discuss.
Logical data flow diagrams (DFDs) present only the logical elements of an information system. By excluding the physical elements, the logical DFD allows us to concentrate on what a system is doing without being distracted by how the f
Physical DFDs present the physical elements of an information system. They concentrate on who is acting on the data flowing through the system. Physical DFDs allow us to concentrate on the entities involved in processing information. We can also see how much “work” is done by an entity by observing the flows into and out of an entity and whether those flows change names, an indication that they have been transformed within the entity.
Finally, a flowchart presents the logical and the physical details of a system's functions. It shows the details of how a process is accomplished and also shows the organizational unit that performs the process. As we will see in Chapter 9, these details are necessary to permit evaluation of a system's controls. Also, systems flowcharts describe exception and error routines, which DFDs do not. DFDs concentrate on usual and recurring events.
In conclusion, it is only with all of these diagrams that we can get a complete picture of a process. As noted above, however, each diagram has it function and, depending on our purpose, all may not be needed.
"It is easier to learn to prepare data flow diagrams, which use only a few symbols, than it is to learn to prepare flowcharts, which use a number of different symbols." Discuss.
Compare the DFD symbols in Figure 4.1 to the flowcharting symbols in Figure 4.6 and you probably conclude that it is quite easy to learn the DFD symbols. Also, examine Figure 4.7 and see that there are several standard routines used in flowcharts. Also, we believe that constructing DFDs presents fewer problems in determining layout and placement of symbols. We conclude, therefore, that DFDs are easier to construct than are flowcharts. You might have a different opinion.
Describe the who, what, where, and how of the following scenario. A customer gives his purchase to a sales clerk, who enters the sale in a cash register and puts the money in the register drawer. At the end of the day, the sales clerk gives the cash and the register tape to the cashier.
The sales clerk performs the data processing activities. The customer and the cashier are entities in the relevant environment.
Give purchase to sales clerk
Enter sale in register (if it is an electronic register, data stores could be updated)
Put money in drawer
4) Give cash and register tape to cashier.
A manual process is performed by the sales clerk using a cash register.
Why are there many correct logical DFD solutions? Why is there only one correct physical DFD solution?
For each sensible grouping of logical activities, there is a correct logical DFD. And, since there are often many sensible groupings, there are multiple correct solutions. However, there is only one correct physical DFD for each system, because these diagrams are constructed directly from a description of the system. There is a one-to-0ne correspondence between entities and bubbles, leaving little or no room for interpretation.
Explain why a flow from a higher- to a lower-numbered bubble on a logical DFD is a physical...
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