Chapter 7 Case Study

Topics: Entity-relationship model, Object, Entity Pages: 2 (518 words) Published: October 11, 2012
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Chapter 7 Case Study -

1. Review the data-flow diagrams you developed for questions in the Petrie’s Electronics case at the end of Chapter 6 (or diagrams given to you by your instructor). Study the data flows and data stored on these diagrams and decide whether you agree with the team’s conclusion that the only six entity types needed are listed in the case and in PE Figure 7-1. If you disagree, define additional entity types, explain why they are necessary, and modify PE Figure 7-1 accordingly.

Answer will vary. Any additional entities should be properly modeled in an E-R diagram similar to Figure 7-1.

2. Again, review the DFDs you developed for the Petrie’s Electronics case (or those given to you by your instructor). Use these DFDs to identify the attributes of each of the six entities listed in this case plus any additional entities identified in your answer to Question 1. Write an unambiguous definition for each attribute. Then, redraw PE Figure 7-1 by placing the six (and additional) entities in this case on the diagram along with their associated attributes.

Answers will vary, according to the answer to Question 1.

3. Using your answer to Question 2, designate which attribute or attributes form the identifier for each entity type. Explain why you chose each identifier.

Answers will vary, according to the answer to Question 1.

4. Using your answer to Question 3, draw the relationships between entity types needed by the system. Remember, a relationship is needed only if the system wants data about associated entity instances. Give a meaningful name to each relationship. Specify cardinalities for each relationship and explain how you decided on each minimum and maximum cardinality at each end of each relationship. State any assumptions you made if the Petrie’s Electronics cases you have read so far and the answers to questions in these cases do not provide the evidence to...
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