Modeling Business Rules - High-Performance Web Databases: Design, Development, and Deployment - page 151

Sometimes the specification of the other rules for a derivative can
become quite complex, involving many rules of basic types (or other deriv-
atives) interconnected in building-block fashion. (Such specification is
called the derivative's template.) If the derivative were not pre-defined, this
template would have to be specified (correctly) for every business rule to
which it applies.
Derivatives are similar to all other rule types in the following ways:
• They must follow rigorous specification conventions, which must be
delineated beforehand. These conventions must be consistent with
the general prescriptions for expressing rules described earlier.
• They must produce a yield value specific to their type. This yield value
may be externalized for use by other rules. (The yield value for a de-
rivative, of course, can be produced from the other rules that com-
prise its template. In this sense, the yield value of a derivative also is
not basic like that of atomic rule types.)
In summary, derivative represents a convenient short-hand (i.e., a single
utility rule type) for some test that appears frequently in business rules, or
that is highly complex, or both. Derivatives represent an important means
by which the set of standard atomic rule types may be extended.
CONCLUSION
Traditional business rule strategies have been inconsistent at best —
making change almost impossible. Turning this trend around requires a
new attitude toward building information systems. To that end, this chapter
described a method for modeling business rules directly, using extensions
to existing data and object models.