Database Reference
In-Depth Information
•
Are both
Employee Identifier
and
Department Code
needed to retrieve a single instance of Employee Phone
Number?
•
Are both
Employee Identifier
and
Department Code
needed to retrieve a single instance of
Department
Phone Number
?
•
Are both
Employee Identifier
and
Department Code
needed to retrieve a single instance of
Organization
Phone Number
?
•
Are both
Employee Identifier
and
Department Code
needed to retrieve a single instance of
Employee First
Name
?
•
Are both
Employee Identifier
and
Department Code
needed to retrieve a single instance of
Employee Last
Name
?
•
Are both
Employee Identifier
and
Department Code
needed to retrieve a single instance of
Department
Name
?
•
Are both
Employee Identifier
and
Department Code
needed to retrieve a single instance of
Employee Start
Date
?
•
Are both
Employee Identifier
and
Department Code
needed to retrieve a single instance of
Employee Ves-
ted Indicator
?
We learned from asking these questions that
Employee Identifier
is needed to retrieve
a single instance of
Employee Phone Number
,
Employee First Name
,
Employee Last
Name
,
Employee Start Date
, and
Employee Vested Indicator
. We learned also that
De-
partment Code
is needed to retrieve a single instance of
Department Name
,
Department
Phone Number
, and
Organization Phone Number
.
Normalization is a process of asking business questions. In this example, we could not
complete 2NF without asking the business “Can an
Employee
work for more than one
De-
partment
at the same time?” If the answer is “Yes” or “Sometimes,” then the first model
under 2NF on the facing page is accurate. If the answer is “No,” then the second model
prevails.
Third Normal Form (3NF)
Recall that the series of rules can be summarized as:
Every attribute is single-valued and
provides a fact completely and only about its primary key
. First Normal Form (1NF) is the
“single-valued” part. Second Normal Form (2NF) is the “completely” part. Third Normal
Form (3NF) is the “only” part.
