Business Information Data Modeling - High-Performance Web Databases: Design, Development, and Deployment - page 233

SUPERTYPE ENTITY: EMPLOYEE

DATA ELEMENTS: EMPLOYEE_NBR

ACTIVE_STATUS_IND
EMPLOYEE_NM
BIRTH_DT

SUBTYPE ENTITY: CURRENT EMPLOYEE RETIRED EMPLOYEE

DATA ELEMENTS: EMPLOYEE_NBR EMPLOYEE_NBR

DEPT_NBR RETIRE_DT

INTERNAL_TEL_NBR

The creation of these additional entities necessitates the maintenance of
business information's referential integrity as defined by their relation-
ships. As a result, business rules must be defined for the relationship
between the supertype and subtype entities or for any relationships with
other entities specific to one of the subtype entities. The same rules exist
for the relationships that now apply to an entity that contains historical
business information. All historical business information, corporately man-
dated audit trails, and time-dependent status changes are business infor-
mation requirements and must be represented in the data model so that
comprehensive understanding is achieved and documented.

EXTERNALLY CONTROLLED BUSINESS INFORMATION

All business information that is depicted in the data model may not orig-
inate in the organization where the data model is constructed. Because the
focus of a data model may be an application, a function, a department, or an
organization, external business information refers to any information that is
not under the control of the area which constructs the data model. When
modeling external business information, the data modeler is inclined to cre-
ate entities for the business information that is received and not for context-
giving entities. For example, when invoices are received from another orga-
nization, an invoice entity may be created. However, no invoice is created
for the entities of the organization that renders the invoice, the billing
account, or the products and services being billed. Only the entity identifier
need be defined for contextual entities because their function is to provide
a framework for the data model's more detailed entities.

Including the contextual entities makes the data model more understand-
able and extensible. In the future, it should be easier to increase the scope
of a data model because the contextual entities may function as building
blocks on which relationships to additional entities can be built. Additional
data elements can also be added to these entities as necessitated by the