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

Silverston c08.tex V2 - 11/21/2008 3:12am Page 456

456 Chapter 8 ■ Business Rules: How Things Should Work

ways. In the level 2 pattern, there was just one classification, namely,

the ENTITY RULE TYPE. Table 8-2 s howed that the instances of PRICE

COMPONENT RULE may be ‘‘Net Price’’ (for maintaining the prices net of

discounts and surcharges under various circumstances) and ‘‘Discount’’ (for

maintaining a discount that may be eitheraflatamountorapercentage).

However, what if you also wanted to maintain a different categorization for

each instance regarding if it was a ‘‘One time price,’’ a ‘‘Recurring charge,’’ or

a ‘‘Utilization charge’’? For example, there could be a need to classify PRICE

COMPONENT RULE instances in several different ways, such as by having a

‘‘Price component nature’’ BUSINESS RULE CATEGORY TYPE with ‘‘Price,’’

‘‘Discount,’’ and ‘‘Surcharge’’ as instances of BUSINESS RULE CATEGORY

and a ‘‘Price component frequency’’ BUSINESS RULE CATEGORY TYPE

with ‘‘One time charge,’’ ‘‘Recurring charge,’’ and ‘‘Utilization charge’’ as

instances of BUSINESS RULE CATEGORY. This would allow you to specify

that a particular rule that specified the monthly charge for a PRODUCT was

classified both as a ‘‘Price’’ BUSINESS RULE CATEGORY and as a ‘‘Recurring

charge’’ BUSINESS RULE CATEGORY. Thus, there would be two instances

of BUSINESS RULE CATEGORY CLASSIFICATION to maintain both of these

classifications. ...