Tài liệu Activity 4.2: Creating a Logical Data Model ppt

Activity 4.2: Creating a Logical Data Model In this activity, you will use the skills learned in this module to define the relationships within a logical data model and produce a sample ER diagram for the Ferguson and Bardell, Inc. case study. In each of the two exercises in this activity, you analyze a single aspect of a logical data design. At the end of each exercise, the class will discuss the design you derived. Objectives After completing this activity, you will be able to: ! Identify relationships between entities. ! Create a logical data model. Before You Begin This activity will take place in small groups with a class discussion following completion of the activity. Prerequisites ! To complete this activity, you need the entities identified in Activity 4.1. Time to complete this activity: 20 minutes 18 Activity 4.2: Creating a Logical Data Model Exercise 1: Identifying Relationships Between Entities In this exercise, you will identify all the relationships between the entities defined in Activity 4.1. ! Identify relationships between entities 1. Join the group to which you have been assigned by the instructor. 2. Review the entities identified in Activity 4.1. Draw a box for each entity in the space below, and label the box with the entity’s name. 3. Place the attributes you identified in Activity 4.1 in the boxes of the corresponding entities. 4. Draw a line between any entities that have relationships. 5. Identify verbs or actions that define the relationship between each pair of entities, and label the line with the relationship verb. This is the initial ER diagram for the logical data model. Answer in v04_1609a_act42-1.bmp Activity 4.2: Creating a Logical Data Model 19 Exercise 2: Determining Cardinality and Existence In this exercise, you will use the syntax discussed in the module to identify the cardinality and existence characteristics of each of the relationships defined in Exercise 1. ! Identify cardinality 1. For each relationship on your ER diagram, ask the question “How many of the parent entity work with how many of the child entity?” This question will help you determine whether the cardinality of each relationship is one-to-one, one-to-many, or many-to-many. 2. Use the syntax discussed in the module to record the cardinality of each relationship and denote the entities as parent or child. ! Identify existence ! For each relationship on your ER diagram, ask the question “Can the child exist if the parent does not exist?” • If the answer is “Yes,” existence is optional. Denote the relationship with a dashed (broken) line. • If the answer is “No,” existence is mandatory. Denote the relationship with a solid line. Answer in v04_1609a_act42-2.bmp Next, you will present your findings to the class. THIS PAGE INTENTIONALLY LEFT BLANK . initial ER diagram for the logical data model. Answer in v 04_ 160 9a_ act42-1.bmp Activity 4. 2: Creating a Logical Data Model 19 Exercise 2: Determining Cardinality. identified in Activity 4. 1. Time to complete this activity: 20 minutes 18 Activity 4. 2: Creating a Logical Data Model Exercise 1: Identifying Relationships