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

Silverston c02.tex V2 - 11/21/2008 2:58am Page 61

Level 3 Declarative Role Pattern 61

has a recursive relationship that states that ‘‘each ROLE TYPE may be classified

by one or more ROLE TYPE(s) and each ROLE TYPE may be within one and

only one ROLE TYPE.’’ This hierarchical structure allows you to support the

classification or organization of the ROLE TYPES. For example, in Table 2-7

you see a hierarchy of different instances of ROLE TYPE. This is illustrated in

Figure 2-7. This recursive relationship also allows maintenance of lower-level

roles. For example, you could also add additional instances to the ROLE TYPE

in order to further break down the roles of customer into ‘‘bill-to customer’’

and ‘‘ship-to customer’’ (although it depends on the circumstances whether

these are actually declarative or contextual roles, as is discussed in Chapter 3).

Table 2-7 Hierarchy of ROLE TYPE(s)

ROLE TYPE. PARENT ROLE TYPE. ROLE TYPE. ROLE TYPE.

ROLE TYPE ID NAME (PARENT) ROLE TYPE ID NAME (CHILD)

100 Party Role 1 Customer

200 Organization Role 2 Supplier

100 Party Role 3 Partner

300 Person Role 4 Employee

100 Party Role 200 Organization Role

100 Party Role 300 Person Role

NOTE

An alternative way to specify which roles are person roles and which are

organization roles is to have subtypes within PARTY ROLE of ORGANIZATION

PARTY ROLE and PERSON PARTY ROLE and then have the roles that are

person-only roles as subtypes ...