Database Reference
In-Depth Information
example,youcaninfertwoconstraintsfromtheresponse:Theminimumnumberofclasses
an instructor can teach is one, and the maximum number is eight. Transform these con-
straints into a business rule by composing a statement such as this one:
Aninstructormustteachoneclass,butnomorethaneightclasses.
After you've defined the rule, continue with the next step.
Step 4: Establish the Rule by Modifying the Appropriate Relationship Characteristics
Establish the business rule you just defined by modifying the appropriate characteristics in
the relationship diagram. Before you make any modifications, consider the business rule
statement once again and identify which relationship characteristics the rule affects:
Aninstructormustteachoneclass,butnomorethaneightclasses.
The constraint affects the number of classes an instructor can teach, so you modify the de-
gree of participation characteristic of the INSTRUCTOR CLASSES table by setting it to
“(1,8).” This rule also affects the type of participation characteristic of the INSTRUCTOR
CLASSES table. You must set the table's type of participation to “Mandatory” because a
single record in the INSTRUCTORS table
must
be associated with at least one record in
the INSTRUCTOR CLASSES table.
Figure 11.10
shows the revised relationship diagram
with your modifications.
