The Data Model Resource Book, Volume 3: Universal Patterns for Data Modeling

Silverston c08.tex V2 - 11/21/2008 3:12am Page 451

Level 3 Business Rules Pattern 451

RULE FACTOR). For example, you may need to influence the price based on

a factor of whether the party has been a customer for between 5 and 10 years.

For this factor, you can maintain a RULE FACTOR TYPE name instance of

‘‘Number of years that party has been a customer’’ with two values: one RULE

FACTOR VALUE factor value of ‘‘5’’ with a FACTOR VALUE TYPE name

of ‘‘Minimum number of years’’ and another RULE FACTOR VALUE factor

value of ‘‘10’’ with a FACTOR VALUE TYPE of ‘‘Maximum number of years. ’’

NOTE

In our experience, many generalized factors have a single value. Also,

some factors that have multiple values can be managed by specifying multiple

factor instances. For example, in the preceding example, we could have had two

RULE FACTOR TYPE(s) of ‘‘Minimum number of years as a customer’’ and

‘‘Maximum number of years as a customer.’’ Thus, an alternative data model

structure is to have a factor value attribute in the BUSINESS RULE FACTOR entity

(as we did in Figure 8-2), instead of maintaining the entity of RULE FACTOR VALUE.

However, the way that we have modeled generalized factors in Figure 8-5 provides

much more flexibility to accommodate many different scenarios.

NOTE

An issue with having generalized RULE FACTOR TYPE(s) and BUSINESS

RULE FACTOR(s) is that not all of the different RULE FACTOR TYPE(s) are applicable ...