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

Silverston c03.tex V2 - 11/21/2008 2:59am Page 122

122 Chapter 3 ■ Using Roles: How Parties Are Involved

generalized PROJECT ROLE/ROLE TYPE structure, for example, ‘‘Technical

Writer’’ as seen in Table 3-15. If you capture ROLE TYPE(s) of ‘‘Project

Worker’’ and ‘‘Project Sponsor’’ in the generalized PROJECT ROLE/ROLE

TYPE structure, we recommend you don’t also maintain these in the specific

PROJECT WORKER, PROJECT SPONSOR structure. Our feeling is that you

should not redundantly capture contextual roles in both the specific way as

well as in the generalized way. You could end up double counting the amount

of people working on a project, for example. Or, if implemented, you would

have the questions of which is the correct way for programmers to code

selecting, inserting, and updating project workers and which is the correct

semantic view for the business as a whole.

The strength of the pattern lies in the fact that you get the benefits of both the

specific Level 2 modeling style and the generalized modeling style of the Level

3 type pattern. When we needed to capture the specific involvement of ‘‘Neena

Davies,’’ she was declared as a WORKER and involved in the PROJECT as a

PROJECT WORKER. When we discovered a new role of ‘‘Technical Writer,’’

we wanted to capture this, but did not want to add new declarative role

entities because that role was not core to XYZ Corporation business. ‘‘Neena

Davies’’ became ...