The Business Unit concept is used to depict a group of roles that perform a common task or share a common characteristic. Business Units usually are chained together using the relationship "Parent" and almost always form a hierarchy. Typically, Business Units consist of a group of individual Roles but may also be formed by a group of sub business units.
Business Units can consists of:
Roles connect to Business Units via the "Member of" relationship and the lowest level of the hierarchy is the Person Concept.
An example: Phil M. has the role Developer which is a Member of the Engineering Department who's parent is Process Tempo.
Below is a Concept Model depicting a more complex scenario: