Rather than having different "kinds" of Principals, I would like to see Roles defined for principals. Both organizations and persons can have roles. Some are specific (e.g. the employee role must be fulfilled by a person, but the employer role may be either a person or organization). Participant roles may be linked by relationships. A person or organization with the customer role is linked to a different person or organization in the supplier role by a relationship between customer and supplier. An organization having the department role may be linked to another organization with the division role in a reporting relationship.

The concept of roles and relationships adds considerable power to Chandler, allowing one to organize contacts and communications in a significantly different way. The concept of a Group may even be replaced by the concept of Relationship, since Groups are Participants having roles linked by relationships. This would also easily permit dynamic membership based on roles and clearly define the purpose of the Group.

I would cite to two references:

• Codd, Lefebvre and De Luca - Java Modeling in Color with UML
• Silverston - The Data Model Resource Book (Volume 1)

-- JimNorman - 16 Mar 2005