A graphical representation of relational formulae with complementation Domenico Cantone, Andrea Formisano, Marianna Nicolosi Asmundo and Eugenio Giovanni Omodeo RAIRO-Theor. Inf. Appl., 46 2 (2012) 261-289 Published online: 27 February 2012 DOI: 10.1051/ita/2012003