Modeling Business Rules - High-Performance Web Databases: Design, Development, and Deployment - page 149

Exhibit 10-7. An inclusion rule.
indicated as the constraining object of another rule. This other rule, called
an inclusion rule, often (but not always) is an enabler or timer. (Very
sophisticated rules may be modeled using rule types other than enablers
or timers as inclusion rules.)
All inclusion rules always effect the interpretation of scope for the con-
straining rule (i.e., for which instances, and in what manner, the rule will be
applied). If the inclusion rule is an enabler or timer, it also may reduce the
scope of the constraining rule by enabling only certain instances, or dis-
abling other. An example illustrates this.
In Exhibit 7, rule #23.1, an enabler, indicates another rule (#23.2) as its
constraining object. This indicates the enabler as being an inclusion rule.
Typically, rule #23.2, an integrity constraint type MANDATORY, would be
enforced for every instance of its constrained object, Order. The inclusion
rule, however, changes this usual interpretation. Specifically, the enabler
switches on (i.e., enables) rule #23.2 for only those orders contained on
express shipments. Those orders on shipments not indicated as express,
or contained on no shipment whatsoever, are not subject to rule #23.2 (i.e.,
rule #23.2 remains disabled for such orders). The inclusion rule acts to
reduce the scope of rule #23.2 (i.e., to reduce the enforcement of rule #23.2
to only selected instances of Order).
Yield Value
Every rule performs some test for instances of the constrained object
and constraining object(s), as indicated by its rule type. This test always
requires these instances to be reflected, evaluated, tallied or computed in
some manner unique to that rule type. For each instance of the rule's con-
strained object, this always produces a single-valued result at any point
in time.