Table Relationships - Database Design for Mere Mortals - page 281

2. Locate the second table on the same side of the matrix you're working on and note
the entry at the junction between it and the first table on the opposite side of the
matrix.
3. Apply the appropriate formula to the two entries and identify the official relation-
ship between the tables.
4. Diagram the relationship in the appropriate manner.
5. Cross out both entries on the matrix.
Now, let's take a look at how you apply this procedure to a pair of tables in the matrix. (In
this example, you're working down the left-hand side of the matrix.)
1. Assume you've selected the BUILDINGS and CLASSES tables. You note that the
entry at the junction between BUILDINGS and CLASSES is 1:N.
2. Now you proceed down the left-hand side of the matrix until you locate the
CLASSES table and then note that the entry at the junction between the CLASSES
and BUILDINGS table is 1:1.
3. Using these entries with the appropriate formula, you determine that the official re-
lationship between the BUILDINGS and CLASSES tables is 1:N. (1:N + 1:1 =
1:N)
4. You create a one-to-many relationship diagram for the BUILDINGS and
CLASSES tables.
5. You cross out the entries on the matrix.
Figure 10.29 shows the results of your work.