Database Reference
In-Depth Information
I would describe the trunk of baseball cards I received as being in a chaotic state as there
was no order to the cards—just a bunch of cards thrown in a large box. I removed the chaos
by organizing the cards. The term
chaos
can be applied to any unorganized pile including
attributes. We may have a strong understanding of each of the attributes, such as their name
and definition, but we don't know to which entity the attribute should be assigned. When I
picked out a 1978 Pete Rose from the baseball card box and put this card in the 1978 pile,
I started bringing order were there was chaos - similar to assigning
Customer Last Name
to the customer pile (called the
Customer
entity).
Let's walk through an example. Here's a bunch of what appears to be employee attributes:
Often definitions are of poor quality or missing completely, so let's assume that this is the
case with this
Employee
entity. We are told, however, that
Employee Vested Indicator
captures whether an
Employee
is eligible for retirement benefits - a value of
Y
for “yes”
means the employee is eligible, and a value of
N
for “no” means the employee is not eli-
gible. This indicator is derived from the employee's start date. For example, if an employee
has worked for the company for at least five years, then this indicator contains the value
Y
,
which means this employee is eligible for retirement benefits.
What is lacking at this point, and what will be solved though normalization, is assigning
these attributes to the right entities.
It is very helpful to have some sample values for each of these attributes, so let's assume
this spreadsheet is a representative set of employee values:
