Database Reference
In-Depth Information
Figure 7.30. Previously unidentified subset tables
Both of these tables represent employees, but each represents a
specific type
of employee.
Notice,however,thattherearegenericfieldscommontobothtables:firstname,lastname,
datehired,streetaddress,city,andstate.Thesefieldsareduplicatedunnecessarily,soyou'll
need to refine the table structures to resolve this problem.
Refining Previously Unidentified Subset Tables
When you identify subset tables such as these, you can refine them using these steps.
1.
Remove all the fields that the subset tables have in common and use them as the
basis for a new
data
table.
2.
Identify what subject the new data table represents, and then give the table an ap-
propriate name.
3.
Make sure that the subset tables represent subordinate subjects of the data table
and modify the subset table names as necessary.
