Getting Started with InfoSphere Data Architect

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72 Getting started with InfoSphere Data Architect Note: If you see warnings in the Problems view, you are not required to fix warnings to create a valid, usable logical data model. Warnings simply let you know when certain analyzed items might be out of compliance or do not conform to standard data modeling rules, but it will not impact the functionality of the model. 3.5 Constraints Now that you have created a couple of entities, you should create some constraints. Constraints are used to enforce business rules for data. First, let's create a constraint that checks to make sure that the student's graduation date is later than the student's start date. This check constraint will make sure that your data is valid when it's entered into the database. To add a constraint to the STUDENT entity: 1. Locate and select the STUDENT entity in the Data Project Explorer: University Info System -> Data Models -> STUDENT_INFO_SYSTEM.ldm -> STUDENT INFO SYSTEM -> STUDENT. 2. Right-click on the STUDENT entity, then select Add Data Object -> Constraint. 3. Name the constraint DATE_CK. 4. Complete the information on the General tab of the Properties view to create a constraint: a. Specify SQL as the language. b. In the Expression field, type GRADUATION_DATE>START_DATE. c. In the Transform As field, specify Check Constraint. The check constraint simply checks that the expression is true. 5. Save your work. 3.6 Exercise Use the process outlined above to expand upon the existing logical data model. Determine the best data type for each attribute, and document each relationship with descriptive verbs. Consider how each entity is related to other entities in the model. 1. Add another entity, ACTIVITY, to describe the clubs and student organizations that each student belongs to. You will use this entity as you complete the other chapters in this book. The entity should include the following required attributes: • STUDENT ID: Stores the student ID number. This is part of the composite key.
Chapter 3 – Logical Data Modeling 73 • ACTIVITY ID: Stores the 5-character ID number of the club or organization. This is part of the composite key. • JOIN DATE: Stores the date that the student joined the organization. 2. Link the STUDENT and ACTIVITY entities with a Non-identifying optional relationship, with a Zero or more cardinality. Use the Details tab to define the relationship of the parent and child entities, and add descriptive verbs to the relationship. 3. Now create one more entity for the logical data model, COURSE. Create the following required attributes: • COURSE ID: Stores the 5-character ID number of the course. This is the primary key of the entity. • DEPT ID: Stores the 4-character ID of the department that runs the course. For example, a course within the English department would have the ENGL prefix. • INSTRUCTOR ID: Stores the 5-character ID of the instructor that is teaching the course. • INSTRUCTOR NAME: Stores the last name of the instructor that is teaching the course. • STUDENT TOTAL: Stores the number of students registered for the course. 4. Link the STUDENT and COURSE entities with a Non-identifying mandatory relationship, with One or more cardinality. Again, use the details tab to describe the relationship between the tables with verbs. Then, link the COURSE and GRADE entities with an Identifying relationship, with a cardinality of exactly one. Document descriptive verbs for each end of the relationship. 5. Remember to save your work. 6. Make sure the diagram reflects the logical data model. When complete, your logical data model should look similar to the image in Figure 3.15.
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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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5 Notices This information was deve
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7 Trademarks IBM, the IBM logo, and
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10 Getting started with InfoSphere
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17 About the Authors Erin Wilson is
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Getting Started with InfoSphere Data Architect

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