All trust groups have the general common trait of having members that are aligned to achieving a vision together. This is done by collaborating on a specification for their system and then agreeing on roles that are responsibilities for various aspects of the system's operations.
In the context of a group working together to achieve a common vision, there is a common process involving the defining of the vision, the assessment of the current state of the group with respect to that vision, and the ongoing reduction of the difference between the current state and the fully realised vision. This process can be thought of as motion and as such it has two general aspects; direction (and distance) and energy.
When defining roles for a trust group, these two common aspects translate into two top level distinct roles; director and manager, the former being responsible for the conceptual state of the group and whether it's heading in the right direction, the later being responsible of the resource allocation and energy/resource aspects of motion toward the goals.