One Concept Equals One Data Element: A Rule for Developing Data Elements - High-Performance Web Databases: Design, Development, and Deployment - page 85

Exhibit 6-9. Nonmutually exclusive valid values.

Data Element Name: EMPLOYEE MARITAL STATUS CODE

Data Element An employee's status with regard to any US state's law

Definition: concerning marriage

Valid Values: M = Married

S = Single
D = Divorced
W = Widowed
L = Legally separated
I = Interlocutory
A = Annulled

values like these, and the matter is usually dealt with by instructing the
people who collect the data (e.g., customers, employees, or data entry
clerks) to pick the choice that best fits. Relying on the data entry clerks or
the people filling out the forms to pick the best choice indicates that some-
one knew that the choices were not mutually exclusive and that the quality
of the data would probably suffer as a result.

Valid values that are not mutually exclusive often are developed for data
elements that encompass more than one concept. In addition, data ele-
ments that include more than one concept are often developed to docu-
ment the effect of implementing several related business rules on an
instance of a business entity. The previous example implements the follow-
ing implicit business rules:

• Only marriages that a U.S. state recognizes as valid are recognized as
valid by the organization.
• Marriages can be legally created and dissolved only by one of the
U.S. states.
• A person can be married to only one other person at a time.
• Once a valid marriage has been dissolved by the state, the persons can
be legally married again.

Many laws define under what circumstances marriages can be dissolved
by annulment or divorce. One data element, EMPLOYEE MARITAL STATUS
CODE, attempts to document the relationship between an employee and all
these business rules. The fact that this data element violates the one-con-
cept-equals-one-data-element rule is evidenced by its valid values. It com-
bines the following concepts: whether or not a person is currently married,
whether or not a person was previously married, and what event caused
the most recent previous marriage to end if the person has not remarried.