I would like you to recommend me a definitive book about concept maps. I've been taking a look to a wide variety but none of them seemed clear to me.
From wikipedia :
A concept map or conceptual diagram is a diagram that depicts suggested relationships between concepts. It is a graphical tool that designers, engineers, technical writers, and others use to organize and structure knowledge.
A concept map typically represents ideas and information as boxes or circles, which it connects with labeled arrows in a downward-branching hierarchical structure. The relationship between concepts can be articulated in linking phrases such as causes, requires, or contributes to.
The technique was first developed in 1970's by Joseph D. Novak. You can try one of his books e.g. Learning, Creating, and Using Knowledge: Concept Maps as Facilitative Tools in Schools and Corporations