bdfd1m0b | Database Administration |
The purpose of normalization is to create tables (also known as relations) for all the entities on which the system holds data. Through the process of normalization, the structure of a table is progressively refined through first, second, and finally third normal form. The following guidelines may be of some help as you develop your tables:
In the context of data normalization, the purpose of the primary key is to identify a unique row in a table. The value of the primary key is always unique.
Each table can have only one primary key, though the primary key itself may be made from more than one attribute.
Unless otherwise stated, the attributes making up the primary key are shown in bold type in the tables.
The concept of the primary key is explained in more detail with the example tables given later in this chapter.
Dependency refers to the relationship of an attribute with the primary key of a table.
To say that an attribute is dependent on the primary key means that, given a particular value for the primary key, there is only one corresponding value for that attribute.
An attribute may be either directly or indirectly dependent on the primary key.
A directly dependent attribute depends on the value of the primary key itself. An indirectly dependent attribute depends on the value of another attribute, which is itself dependent on the primary key. This indirect dependency is sometimes called transitive dependency.
The concept of dependency is further explained with the example tables given later in this chapter. See especially Second Normal Form.