Database Reference
In-Depth Information
By using the same steps, you can create other nonspeciic relationships.
4. Creating recursive relationship : In the class registration data model, there is a many-
to-many recursive relationship. he intersection entity is COURSE_PREREQUISITE.
he following are the steps to show you how to create the recursive relationship.
Suppose that both the COURSE and the COURSE_PREREQUISITE entities
in Figure 2.12 have been created. Click Connector Tool on the tool bar. Move
the mouse cursor over the parent entity COURSE . When a red rectangle appears,
press the mouse. hen, hold the mouse and move the cursor over to the child
entity COURSE_PREREQUISITE . When a red rectangle appears, release the
mouse.
Move the mouse cursor over the parent entity COURSE again. When a red rect-
angle appears, press the mouse. hen, hold the mouse and move the cursor over
to the child entity COURSE_PREREQUISITE . When a red rectangle appears,
release the mouse.
While the second relationship connector is selected, make sure that Deinition
is selected in the Categories pane. In the Parent: COURSE list box, select
CourseID and select Prerequisite in the Child list box. Click the Associate but-
ton to associate CourseID to Prerequisite (Figure 2.30).
To conigure the cardinality, click the irst relationship connector line. In the
Database Properties dialog, select Miscellaneous in the Categories pane. Check
the cardinality option One or more . Do the same for the second connector line.
Create data model : Now, you have created all the entities and the relationships that
associate them. By connecting the components together, you can form a data model shown
in Figure 2.31.
Figure 2.31 shows the E-R model for the class registration process. he data model
includes entities, attributes, and relationships. he entity CLASS has the most relationships.
his type of entity is called a central entity .
he above case study has been used to demonstrate the process of developing a data
model. It is for illustration purposes only. A real-world registration system can be much
more complicated.
Figure 2.30
Associate CourseID to prerequisite.
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