LOGICAL DATABASE DESIGN - Fundamentals of Database Management Systems - page 177

Salesperson Number Salesperson Name
Salesperson Number Commission Percentage
Salesperson Number Year of Hire
Salesperson Number Department Number
Salesperson Number Manager Name
Product Number Product Name
Product Number Unit Price
Department Number Manager Name
Salesperson Number, Product Number

F IGURE 7.27
List of defining associations (functional
dependencies) for the attributes of
salespersons and products

Quantity

demonstrating one step of the data normalization process, is that Manager Name
is defined, independently, by two different attributes: Salesperson Number and
Department Number:

Salesperson Number Manager Name

Department Number Manager Name

Both these defining associations are true! If I identify a salesperson by his
Salesperson Number, you can tell me who his manager is. Also, if I state a
department number, you can tell me who the manager of the department is. How
did we wind up with two different ways to define the same attribute? Very easily!
It simply means that during the systems analysis process, both these equally true
defining associations were discovered and noted. By the way, the fact that I know
the department that a salesperson works in:

Salesperson Number Department Number

(and that each of these two attributes independently define Manager Name) will
also be an issue in the data normalization process. More about this later.

Steps in the Data Normalization Process
The data normalization process is known as a ''decomposition process.'' Basically,
we are going to line up all the attributes that will be included in the relational
database and start subdividing them into groups that will eventually form the
database's tables. Thus, we are going to ''decompose'' the original list of all of
the attributes into subgroups. To do this, we are going to step through a number
of normal forms. First, we will demonstrate what unnormalized data looks like.
After all, if data can exist in several different normal forms, then there should be
the possibility that data is in none of the normal forms, too! Then we will basically
work through the three main normal forms in order:

FirstNormalForm
Second Normal Form
Third Normal Form

There arc certain ''exception conditions'' that have also been described as normal
forms. These include the Boyce-Codd Normal Form, Fourth Normal Form, and
Fifth Normal Form. They are less common in practice and will not be covered here.