Database Reference
In-Depth Information
Figure 10.27. Completed table-matrix entries for the CLASSES table
You've probably noticed that some of the junction boxes are empty; this is perfectly ac-
ceptable. It's unnecessary for you to enter anything into the junction box if there is no rela-
tionship between the tables at either end of the junction.
Now you repeat this process for each table on the left-hand side of the matrix. Remember
that you can start with any table. Let's assume that you decide to continue with the
BUILDINGS table, and you're attempting to identify the relationship between it and the
CLASSES table. Yes, I know you've covered this once already, but in this case you're
identifying the relationship
from the perspective of the
BUILDINGS
table.
Let's now as-
sume that you ask this question:
Does a single building provide space for more than one class?
Iftheanswerisyes,thenaone-to-manyrelationshipexistsbetweenthesetables;otherwise,
it'saone-to-onerelationship. Onceyou'veidentified therelationship, indicate therelation-
ship type in the box located at the junction of the BUILDINGS table row (on the left) and
the CLASSES table column (on the top).
Figure 10.28
shows the revised table matrix with
your entries for the BUILDINGS table.
