[James --- wrong kind of graph.]

Ines, 

Can you be more explicit in your question?  Perhaps sketch a simple example.

Ben

Thanks you for your answers.

I am modelling knowledge with graphs and i need to classify my knowledge on sub-graphs where each graph represents a completeness level of the graph.

Is it more clear? In fact i am looking to do clustering without duplicating my nodes.

Thank you a lot for your answers. I was looking also to hypergraphs http://en.wikipedia.org/wiki/Hypergraph. Do you think that they could be a solution for my problem ?

Just a different perspective on Stefan's answer: hypergraphs would be projections of the incidence relation of the concept graph, so you would be losing structure by using them. 

Incidentally, if you haven't seen it already, the Applications book that Stefan linked has a paper dealing directly with Conceptual Graphs and FCA.

Please see the following link.

J F Sowa - Conceptual Graphs  - http://www.jfsowa.com/cg/cg_hbook.pdf