Tuning the Schema - Professional SQL Server 2005 Performance Tuning - page 195

Note that in the License and Frequency tables there's no reference of the other table's key. This is because
License and Frequency have a many-to-many relationship with each other. This means that many license
classes can reference many frequency values. Likewise, many frequency values can reference many
license classes. The only way to accommodate these relationships is through the use of a third table. This
table will contain nothing but the key columns of both base tables. Hence, a LicenseFrequency table with
the structure shown in Figure 8-5.
Figure 8-5
Thus, the final structure as shown in Figure 8-6.
Figure 8-6