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

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

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

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

! 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

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