

Subject1
|--subtopic1--books
____________--URLs
Subject2
|__subtopic2--books
|___________--URL
|__subtopic3--books
|___________--URL
Doing it in Book and Link (top category) would mean duplicating all the subtopics. See the dilemma?

I will try out the discograph module and see if that help.
It would be great if future XOOPS would allow a means to duplicate module. Many users are asking for the CLONE feature.

In that case, I can rename the LINK module as Book Lists, or Web Links.