Systems Analysis and Design, Tenth Edition End of Chapter Solutions. CHAPTER 5 Data and Process Modeling

IT 510 Systems Analysis and Design, Tenth Edition End of Chapter Solutions. CHAPTER 5 Data and Process Modeling Chapter Exercises s Questions 1. Describe data and process modeling concepts and tools. Data and proc ...

IT 510 Systems Analysis and Design, Tenth Edition End of Chapter Solutions. CHAPTER 5 Data and Process Modeling Chapter Exercises s Questions 1. Describe data and process modeling concepts and tools. Data and process modeling is a process-centered approach because it focuses on the flow of data and the processes that affect that data. Data and process modeling produces a logical model of a business information system by examining the system’s inputs, outputs, and processes, and by focusing on the flow of data through the system. Because users and managers often think in terms of business processes, they find it easy to relate to a processcentric approach. The three main data and process modeling techniques are DFDs, the data dictionary, and process description tools. Data flow diagrams (DFDs) show the flow of data through an information system in a graphical, top-down fashion. The data dictionary documents the contents of data flows, data stores, external entities, and processes. Process description tools include structured English, decision tables, and decision trees. Structured English is a subset of standard English used to describe logical processes clearly and accurately. A decision table is a tabular description of a logical structure. A decision tree is a horizontal graphic representation of a logical structure. (Page 184) 2. Explain the differences between Gane and Sarson and Yourdon symbols. Provide examples of symbols that represent processes, data flows, data stores, and entities.  The Gane and Sarson symbol for a process is a rectangle with rounded corners, while the Yourdon symbol is a circle. The name of the process is placed inside the symbol.  Both symbol sets show a data flow as a line with an arrowhead, with the name of the data flow placed above, below, or alongside the line. The line’s arrowhead shows the direction in which the data flows.  The Gane and Sarson symbol for a data store is a flat rectangle open on the right side. The Yourdon symbol is two parallel lines. The name of the data store is placed inside the symbol.  An external entity is a person, department, outside organization, or other information system that provides data to the system or receives output from the system. The symbol for an external entity in both sets is a square. The Gane and Sarson symbol usually is shaded, and the name of the external entity is placed inside the symbol. Systems Analysis and Design, Tenth Edition Page 2 of 49  Examples of process names are APPLY RENT PAYMENT, CALCULATE COMMISSION, ASSIGN FINAL GRADE, VERIFY ORDER, and FILL ORDER.  Examples of data flow names are DEPOSIT, INVOICE PAYMENT, STUDENT GRADE, ORDER, and COMMISSION.  Typical data store names might include PAYROLL ITEMS, CLASS ROSTER, INVENTORY LIST, and COURSE SCHEDULE  Some examples of entity names might be CUSTOMER, BANK, VENDOR, or ACCOUNTING SYSTEM. (Page 184, 189) 3. What is the difference between a context diagram and diagram 0? Which symbol is not used in a context diagram? The context diagram contains only one process symbol, process 0, which represents the entire system. Diagram 0 is a more detailed (or exploded, partitioned, or decomposed) version of process 0 on the context diagram. The major processes, data flows, and data stores for the information system are shown on diagram 0. The data store symbol is not used in a context diagram. Use a data store only when two or more processes use that data store. Otherwise, the data store is internal to a process and not visible from the outside. Because a context diagram involves only one process, all data stores are internal to that process and do not appear in the context diagram. (Page 192, 193) 4. How would you explode DFDs? An exploded data flow diagram is a more detailed or expanded version of a higher-level process. To explode DFDs, you would create a lower level of diagrams that provide the inner details for processes shown in the higher-level diagrams. (Page 213) 5. Describe a data dictionary and list the types of information it contains. A data dictionary is a central storehouse of information about the system’s data. An analyst uses the data dictionary to collect, document, and organize specific facts about the system, including the contents of data flows, data stores, entities, and processes. The data dictionary also defines and describes all data elements and meaningful combinations of data elements. During enterprise modeling, the data dictionary documents the contents of data flows, data stores, external entities, and processes that appear in the information system's data flow diagrams. (Page 197) 6. How would you level DFDs? Leveling also is called exploding, partitioning, or decomposing. Leveling describes the technique of representing the graphical model of an information system first as a single process, and then in greater and greater detail, until all processes are functional primitives. (Page 196) 7. How would you balance DFDs? A balanced data flow diagram is one that has the input and output data flows of the parent process preserved on the child data flow diagram. To be sure it is correct, you would check carefully to see that these flows are the same. This is called the “black box” concept – the wires going in and out are the same, but you cannot see what goes on inside the box until you explode the DFD. For example, refer to Figure 5-19 on page 199 for a good example of this concept, as shown below: Systems Analysis and Design, Tenth Edition Page 3 of 49 8. What is the purpose of decision tables? How do you create them? A decision table describes a logical structure. To create a decision table, you would: a. Place a heading at the top left that names the table. b. Enter the conditions under the heading, with one condition per line, to represent the customer status and availability of products. c. Enter all potential combinations of Y/N (for yes and no) for the conditions. Each column represents a numbered possibility called a rule. d. Place an X in the action entries area for each rule to indicate the outcome of the rule. (Page 210) Systems Analysis and Design, Tenth Edition Page 4 of 49 9. Why would a manager prefer a decision tree instead of a decision table? Decision trees and decision tables provide the same results, but in different forms. As the chapter points out, a decision tree is a graphical representation of the same conditions, actions, and rules found in a decision table. Decision trees show the logic structure in a horizontal form that resembles a tree with the roots at the left and the branches to the right. Like flowcharts, decision trees are useful ways to present the system to management. In many situations, a graphic is the most effective means of communication. Like a decision table, a decision tree illustrates the action to be taken based on certain conditions, but presents it graphically. Whether to use a decision table or a decision tree often is a matter of personal preference. A decision table might be a better way to handle complex combinations of conditions. On the other hand, a decision tree is an effective way to describe a relatively simple process. (Page 214) 10. What is structured English? Structured English is a subset of standard English used to describe logical processes clearly and accurately. (Page 209) Discussion Topics 1. Suppose you were assigned to develop a logical model of the registration system at a school or college. Would you be better off to use a top-down approach, or would a bottom-up strategy be better? What would influence your decision? The textbook points out that most analysts use a top-down model. They create the context diagram, then diagram 0, then all the child diagrams for diagram 0, and so on. Other analysts follow an alternative bottom-up strategy. With a bottom-up strategy, you first identify all functional primitives, data stores, external entities, and data flows. Then group processes with other related symbols to develop the lowest-level diagrams. Next, group those diagrams in a logical way to form the next higher level. Work up until you reach diagram 0. There is no single answer to this question. Regardless of which strategy used, apply the suggestions and guidelines discussed in this chapter. The main objective is to ensure that your model is accurate and easy to understand. 2. Some systems analysts find it better to start with a decision table, and then construct a decision tree. Others believe it is easier to do it in the reverse order. Which do you prefer? Why? By now, students should see pros and cons both ways. They should realize that the answer might depend on the audience and the complexity of the process description. Divide the group into teams, and ask them to present the best arguments in a debate format. 3. A systems analyst attended a week-long workshop on structured analysis. When she returned to her job, she told her boss that structured analysis was not worth the time to learn and use on the job. Her view was that it was too academic and had too much new terminology to be useful in a practical setting. Do you agree or disagree? Defend your position. Students typically support both positions. There are some arguments for agreeing with the systems analyst's viewpoint. First, if the organization already has a systems analysis methodology that works effectively, there is no reason to introduce a new approach. Second, just because some people find structured analysis to be useful does not mean that the organization will find it to be useful. Systems Analysis and Design, Tenth Edition Page 5 of 49 Third, learning and adopting any new method involves time and cost, which need to be identified and allocated. Fourth, before the introduction of structured analysis, other systems analysis methodologies were used, so there probably will be other new approaches in the future to replace structured analysis. Some arguments for disagreeing with the systems analyst's viewpoint follow. First, many companies use structured analysis and many experts endorse this approach, so structured analysis must be an effective approach. Second, if the company currently does not have a standard systems analysis methodology, structured analysis is as good as any methodology, and a standard approach would be beneficial to the company. Third, learning something new is good, even if the company only ends up questioning what they currently do and how they do it. Fourth, the company must keep up-to-date in order to handle Web-based research, understand technology developments, and communicate effectively with other IT professionals. 4. This chapter describes a black box concept that allows more detail to be shown as a process is exploded. Can the concept be applied in business management generally, or is it limited to information systems design? Provide some reasons and examples. Modular design concepts can be applied in any situation. Students should understand that a modular approach simply breaks tasks or processes down into smaller units that easily can be rearranged, reassigned, and managed. In Chapter 3, students learned about project management, and they can see how tasks are broken down into basic units that can be measured and tracked. A familiar example of modular design might be prefabricated roof trusses that can be lifted into place and tied into a home construction system. Similarly, an auto manufacturer might use the same ignition module for several models. A child playing with a Legos set is an excellent example of flexible modular design at work. Projects 1. Draw a context diagram and a diagram 0 DFD that represents the information system at a typical library. You might suggest that students start with an FDD to identify the major functions before they create the DFDs. A sample FDD follows: Students should be able to create a basic context diagram, using their personal experience Systems Analysis and Design, Tenth Edition Page 6 of 49 and understanding of library functions. Their Diagram 0 DFDs will depend on the context diagram they created. Here is a sample diagram 0: 2. On the Internet, locate at least three firms that offer CASE tools as shareware or free, public domain software. Describe what you found. Part B of the Systems Analyst’s Toolkit lists many CASE tool vendors. Students can visit vendor Web sites to determine whether demonstration copies or student versions are available. In most cases, companies respond promptly to e-mail requests for product information. This is an easy task, and you could enhance it by adding more requirements and an element of competition. 3. Create a decision table with three conditions. You can make one up, or use a scenario from everyday life. Either way, be sure to show all possible outcomes. Students should be able to suggest many situations where several conditions control the outcome. Some suggestions might be course prerequisites (and possible waivers) that determine whether a student can take a particular course; various discounts that can (or cannot) be combined to change the price at a retail store; or a company policy that allows an employee to take sick leave if he or she has enough seniority and accumulated sick leave time. 4. The data flow symbols shown on page 185 were designed by Ed Yourdon, a well-known IT author, lecturer, and consultant. Many IT professionals consider him to be among the most influential men and women in the software field. Learn more about Mr. Yourdon by visiting his Web site at www.yourdon.com, and write a brief review of his work. Systems Analysis and Design, Tenth Edition Page 7 of 49 This is an excellent opportunity for students to learn more about one of the leading figures in the IT world. Mr. Yourdon has been extremely influential and has made an enormous contribution to IT modeling and systems design concepts.