The book co-edited by SimonBuckinghamShum
Visualizing Argumentation is written by practitioners and researchers for colleagues working in collaborative knowledge media, educational technology and organizational sense-making. It will also be of interest to theorists interested in software tools which embody different argumentation models. Particular emphasis is placed on the usability and effectiveness of tools in different contexts.
Chapter on diagrams : http://kmi.open.ac.uk/publications/papers/kmi-tr-25.pdf