Getting Started with InfoSphere Data Architect

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60 Getting started with InfoSphere Data Architect Figure 3.8 – Complete STUDENT entity 3.2.2.7 Creating entities in the Data Project Explorer Let's use the Data Project Explorer view to create a new entity, GRADE to store information about student grades. To create entities with the Data Project Explorer view: 1. Locate the STUDENT_INFO_SYSTEM.ldm data model in the Data Project Explorer by expanding the folders in the project: University Info System -> Data Models -> STUDENT_INFO_SYSTEM.ldm. 2. Create the GRADE entity: a. Right-click the STUDENT INFO SYSTEM package under the logical data model, then select Add Data Object -> Entity. b. Name the new entity GRADE by making sure the entity is selected in the Data Project Explorer, then open the General tab of the Properties view and change the name and label to GRADE. The entity is created under the STUDENT INFO SYSTEM package. Note that the entity does not appear in the diagram editor. This is because you did not create the entity within the diagram. Only objects that you create or drag to the diagram appear in the diagram editor. To better visualize how the data is connected, add the entity to the diagram. 3. Add the new entity to the diagram: a. Select the GRADE entity in the Data Project Explorer. b. Drag the entity from the Data Project Explorer to a blank space in the diagram editor. When you release the mouse button, the entity is added to the diagram. 4. Select the GRADE entity. 5. Add the following attributes to the GRADE entity:
Chapter 3 – Logical Data Modeling 61 • STUDENT ID: Use the same properties that you used to create the STUDENT ID attribute for the STUDENT entity. • COURSE ID: Use the CHAR(8) data type. This is also a primary key. • SCORE PASSFAIL: Use the BOOLEAN data type. This attribute is required. • SCORE TOTAL: Use the DECIMAL data type, with a length/precision of 3 and a scale of 0. This attribute is required. You have created the GRADE entity. In some cases a composite key is needed. A composite key is a primary key that is made up of more than one attribute. Composite keys help make sure that your primary keys are always unique without duplicating existing attributes. For example, to make the GRADE entity unique, you need a composite primary key: STUDENT ID and COURSE ID. This is shown in Figure 3.9. Figure 3.9 – Creating a composite key in the Properties view Note: When you delete objects from the diagram, they are not deleted from the data model. Use the Data Project Explorer to remove data objects from your data models. 3.2.3 Adding relationships Now that you have created the two entities in this diagram, you need to specify how the entities are related. Since the information in this model is related to the student, the STUDENT entity is the parent entity. Just as you can create entities within the diagram, you can also specify the relationships between data objects by using the diagram editor. Relationships types are identifying and non-identifying. In an identifying relationship, one of the child entities is a dependent entity. A dependent entity is an entity whose existence is based on the existence of another set of entity. A non-identifying relationship is one in which both entities are independent (also known as strong relationship set). Create a non-identifying optional relationship between the STUDENT entity and the GRADE entity:
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G E T T I N G S T A R T E D W I T H
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