Database Reference
In-Depth Information
First Normal Form (1NF)
. Removes repetition by creating one-to-
many relationships between master and detail entities, as shown in
Figure 1.8.
Note:
An entity is synonymous with or the same thing as a table.
Second Normal Form (2NF)
. Creates many-to-one relationships
between static and dynamic entities, as shown in Figure 1.9.
Third Normal Form (3NF)
. Can be used to resolve many-to-many
relationships into unique values, as shown in Figure 1.10. This is
where Normal Forms begin to become a bit of a gray area. Sometimes
many-to-many 3NF entities are what I like to call many-to-many join
resolution entities. Many-to-many join resolution entities are often
not utilized by applications and are usually superfluous. Always be
sure that a many-to-many join resolution entity is actually required.
One simple method of being sure that these entities are useful is that
they have a meaningful name. The more entities that are created in a
data model, the more complex SQL code joins will become. Contrary
Figure 1.9
Second Normal
Form (2NF).
