Scenario-Based Techniques for Supporting the Elaboration and the Validation of Formal Requirements PATRICK HEYMANS Institut d’Informatique, University of Namur Rue Grandgagnage 21, B-5000 Namur, Belgium Patrick.Heymans@info.fundp.ac.be ERIC DUBOIS S.W.I.F.T, Avenue Adèle 1, B-1310 La Hulpe, Belgium Eric.Dubois@swift.com CREWS report 98-30 Technical Report of the University of Namur October 1998 This is a draft version of a paper published in the Requirements Engineering Journal (1998) 3:202-218, Springer-Verlag .