Petrie’s Electronics Case Questions Solutions

Again, review the DFDs you developed for the Petrie’s Electronics case. (I have placed the level 1 diagrams in the Project Workbook – Week 3 folder in doc sharing, use your homework solution for the Record Customer Activities level 1).

Use these DFDs to identify the attributes of each of the six entities listed in this case, using Figure PE Figure 7-1; I have also placed the Visio diagram in doc sharing, Project Workbook – Week 4).

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.

List at least 2 attributes for each of the six entities and describe then in a short sentence or bullet statement. Then redraw PE Fig 7-1 to look like figure 7-21.




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

Look in the book for the definition of an identifier – an attribute that will make each entity unique (sometimes called candidates Key or primary keys; i.e. student ID etc.). Pick an identifier for each of the six entities that will make them unique. Identifiers are underlined in attribute list in entities – so look in the book for some examples)



  1. 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 on 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 justify the cardinalities you choose. Redraw your final E-R diagram in Microsoft Visio

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