Groups are collections of roles. In this way, it is possible assign multiple roles to participants in a single step. Groups may also contain other groups.
Unlike an organizational unit, which can belong to only one parent organizational unit, a group may be included in many other groups. Groups are therefore not organized in a hierarchical structure. However, if a group is included in another group, then it cannot have as a member that group. That is, so long as group A includes group B, group B cannot include group A.