Databases Reference
In-Depth Information
Figure 4-24
Salesperson Number
Salesperson Number
Salesperson Number
Salesperson Number
Salesperson Number
Product Number
Product Number
Department Number
Salesperson Number, Product Number
Salesperson Name
Commission Percentage
Year of Hire
Department Number
Manager Name
Product Name
Unit Price
Manager Name
Quantity
Salesperson entity defining associations (functional dependencies).
ticular Product Number defines or specifies a particular Quantity. Put another
way, in this business context, we know how many units of a particular product
a particular salesperson has sold.
Another point, which will be important in 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
Manager Name
Both of these defining associations are true. If you identify a salesperson by
Salesperson Number, you can determine the salesperson's manager. Also, given
a department number, you can determine the department manager. What this
means is that during the systems analysis process, both of these equally true
defining associations were discovered and noted. By the way, the fact that we
know the department that a salesperson works in:
Salesperson Number
Department Number
→
Department Number
(and that each of these two attributes independently defines Manager Name) is
also an issue in the data normalization process.
→
4.3.2 Normalizing Data by the Numbers
The data normalization process is known as a
decomposition process,
some-
times called
non-loss decomposition.
We will line up all of the attributes to 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 the attributes into subgroups. To do so, we are going to step
