Getting Started with InfoSphere Data Architect

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: