I think the above descriptions of relational segments are a little confusing and inaccurate.
Using Michael's example of students in a class modeled as an acs group, you might create a new relationship type 'learning' for students and another type 'teaching' for professors. Both students and professors are now members of the group, and you can treat them as a whole for purposes of permissions, spam etc.
It is also useful to treat the students and professors as seperate groups, for example to assign professors some extra privilege such as bboard admin. You could create a new group and add the professors, making sure to keep membership in both groups in sync, or you can use relational segments.
Relational segemnts define the members of a group based on some existing relationship they have to another group.
