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1、Data flow diagrams and flowcharts provide redundant pictures of an information system. We dont need both. Discuss.ANS. 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

2、system is doing without being distracted by how the functions are being performed and by whom. 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 involve

3、d 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

4、 of a systems 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 systems controls. Also, systems flowcharts describe exception and error

5、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.DQ4-2 It is eas

6、ier 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.ANS. 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 t

7、he 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.

8、 You might have a different opinion.DQ4-3 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

9、register tape to the cashier.ANS. Who = The sales clerk performs the data processing activities. The customer and the cashier are entities in the relevant environment. What = （1） Give purchase to sales clerk（2） Enter sale in register （if it is an electronic register, data stores could be updated） （3

10、） Put money in drawer（4） Give cash and register tape to cashier. Where = Store. How = A manual process is performed by the sales clerk using a cash register.DQ4-4 Why are there many correct logical DFD solutions? Why is there only one correct physical DFD solution?ANS. For each sensible grouping of

11、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

12、one-to-0ne correspondence between entities and bubbles, leaving little or no room for interpretation.DQ4-5 Explain why a flow from a higher- to a lower-numbered bubble on a logical DFD is a physical manifestation of the system. Give an example.ANS. If we feel that we must send a data flow from one b

13、ubble on a logical DFD to a bubble on that diagram with a lower number, then we must have a picture in our mind of that lower-numbered bubble as a person, place, or thing rather than a logical activity. If you have such a picture, your diagram will represent a physical description of the system, reg

14、ardless of the labels that we might assign to the flows and to the bubbles. Lets use Figure 4.11 for an example. If in that DFD we sent the data flow Cash receipts total to bubble number 2.0, we would have a physical data flow. Perhaps we included such a flow because we picture bubble 2.0 as a place

15、 rather than as a function. That would be a mistake in constructing a logical DFD.DQ4-6 Compare and contrast the purpose of and techniques used in drawing physical DFDs and logical DFDs.ANS. We draw physical DFDs to depict a systems entitiesboth internal and externaland to characterize the communica

16、tions between those entities. We draw logical DFDs to describe the functionsor information processing activitiesperformed by the system. We use the same symbols for drawing logical and physical DFDs. However, the way we use those symbols differs. In a physical DFD, the bubbles are labeled with the n

17、ames of entities, while in a logical DFD, the labels describe the functions being performed. In a physical DFD the labels on the data flows and on the data stores are actual specific names that describe the method used for communicating and for storing the data, while in a logical DFD, those labels

18、are generic descriptions or names that describe the data.DQ4-7 If we document a system with a system flowchart and data flow diagrams, we have over-documented the system.ANS. We dont agree with this statement. Each tool documents a different aspect of a system and is used for a different purpose A s

19、ystems flowchart depicts a systems information and operations activities and superimposes those activities onto the organizations structure. We use the flowchart to understand the systems activitiesboth information and operationsand to analyze the systems controls. Data flow diagrams concentrate on

20、the data, the entities that act on the data, and the information systems functions being performed by a system. We use the DFDs to analyze each of these elements of a system. Also, we use the logical DFD extensively in the development of new systems.DQ4-8 Preparing a table of entities and activities

21、 as the first step in documenting systems seems to be unnecessary and unduly cumbersome. It would be a lot easier to bypass this step and get right to the necessary business of actually drawing the diagrams. Do you agree? Discuss fully.t agree. With practice, preparation of a table of entities and a

22、ctivities is not difficult. Also, we find that we prefer to prepare this table before drawing any diagrams because the table helps us to lay out the diagrams and to avoid mistakes and minimize the need for redrawing.DQ4-9 In terms of the sequence used in documenting systems, it would be easier to pr

23、epare a systems flowchart before we prepare data flow diagrams.t agree. Those of you familiar with flowchartsand not familiar with DFDsmight prefer to start with a flowchart. However, our experience is that a flowchart is the most difficult of the diagrams to draw because: the flowchart uses many mo

24、re symbols than the other diagrams, must be carefully laid out, and may require complicated on- and off-page connectors. After completing the table of entities and activities and the DFDs, we have found that completing a systems flowchart is relatively uncomplicated.DQ4-10 Since there are computer-b

25、ased documentation products that can draw data flow diagrams and systems flowcharts, learning to draw them manually is a waste of time.ANS. We disagree, partly. We have used computer-based documentation packages and believe that you must know something about drawing DFDs and flowcharts before you ca

26、n use such packages effectively. However, you might develop your documenting skills by using such a package rather than by practicing manual diagram preparation. The faculty in our English department believes that students can be better writers, if they learn to write using a word-processing package

27、. Perhaps students would prepare better documentation if they were to learn to prepare DFDs and flowcharts while using a documentation package.ProblemsNOTE TO INSTRUCTORS: Additional problems can be created from the diagrams and solutions for Problems 4-1 through 4-3. First, you could provide the st

28、udents with the narrative and a partially completed diagram requiring that the students fill in the missing parts of the diagram. Or, you could provide the diagram and a partially completed narrative and require that the students fill in the blanks in the narrative.P4-1 ANS. At the Companys sales of

29、fice, sales representatives answer customer calls and enter customer orders into the computer. The computer accesses the Inventory master data （on disk） to determine the availability and prices for the items requested. Also, the computer accesses the Customer master data （on disk） to determine the c

30、ustomers credit limit and compares that limit to the balance outstanding on the Accounts receivable master data （on disk） and to the amount of the order. Next, the computer updates the inventory master data and notifies the clerk that the order has been accepted. The clerk notifies the customer by p

31、hone. Also, the computer prints a two-part picking ticket on a printer located in the warehouse. In the warehouse, clerks annotate the picking ticket （we assume that it is annotated with the quantities picked）, file copy 2 in the warehouse and send copy 1 to shipping （we assume that it is sent along

32、 with the goods）. In shipping, clerks prepare a two-part packing slip, file copy 2 with the annotated picking ticket and give copy 1 to the carrier （we assume that the packing slip is attached to the goods）.P4-2 ANS. Potential customers contact this company with a request for services. A contract is prepared and filed in the Contract file