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as numeric and when the physical domain is changed to character at some
later date. The existing database structures must be redefined, the business
information must be converted, and all application programs that expect a
numeric data type must be changed.
If all externally controlled data elements are defined as having a charac-
ter physical domain to minimize the impact of future changes, however,
calculations can no longer be performed. The physical domain should be
chang6d to character if the data element is used as an identifier or indica-
tor (e.g., customer number). The valid range of numeric values can be
enforced through application logic. If the data element is a dollar amount
or a numeric field that may be used in a calculation, the physical domain
should not be changed. This approach prevents most conversion efforts
because the numeric fields that are used as identifiers are the most likely
ones to change to character.
Business information that originates from an external organization pre-
sents some unique challenges for the data modeler. This business informa-
tion cannot be controlled and may cause problems for entity identifier def-
initions and data element physical domains. Understanding exactly which
business information is received concerning its definition, level, and use
and designing additional entities that create a context for it helps the orga-
nization to achieve a comprehensive data model.
SUMMARY
Some business information is easy to model and other information may
be more difficult. Regardless of its difficulty to model, the data modeler
must include all business information in the data model to be able to
develop a data model that represents a comprehensive understanding of
the business information requirements. To develop such a data model, the
data modeler must have a thorough understanding of the business infor-
mation and its meaning and with this knowledge, no business information
is impossible to model.
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