A tree is a natural structure, because often you respond to another post. A graph would mean responding to several posts, which doesn't happen that often. Usen

A tree is a natural structure, because often you respond to another post. A graph would mean responding to several posts, which doesn't happen that often. Usenet discussions have an additional structure on top of the answer-tree: You can group discussions by subject/topic, changing the subject line when the subject changes. So that would be a colored graph. Good Usenet readers have a lot more features (e.g. marking posts as read, killfiles) than anything that web-based discussions offer. I sometimes wish that web UI's would implement this, too.