Int. J. Web and Grid Services, Vol. 7, No. 1, 2011 91 CPN-TWS: a coloured petri-net approach for transactional-QoS driven Web Service composition Yudith Cardinale* Universidad Simón Bolívar, Venezuela E-mail: yudith@ldc.usb.ve Website: http://www.ldc.usb.ve/∼yudith *Corresponding author Joyce El Haddad and Maude Manouvrier Université Paris-Dauphine, LAMSADE, France E-mail: elhaddad@lamsade.dauphine.fr E-mail: manouvrier@lamsade.dauphine.fr Website: http://www.lamsade.dauphine.fr/∼elhaddad Website: http://www.lamsade.dauphine.fr/∼ manouvri Marta Rukoz Université Paris Ouest Nanterre La Défense LAMSADE – Université Paris-Dauphine, France E-mail: Marta.Rukoz@dauphine.fr Website: http://www.lamsade.dauphine.fr/ scripts/publis.php?author=rukoz Abstract: In this paper, we address the issue of selecting and composing Web Services (WSs) considering functional and Quality of Service (QoS) requirements combined with transactional properties. We formalise the WS functional, QoS and transactional properties as well as the WS Composition problem. We have extended Coloured Petri Net (CPN) formalism to incorporate transactional WSs properties in the composition process. We present and prove our CPN Transactional WS (CPN-TWS) selection algorithm that satisfies the user query functional conditions expressed as input and output attributes, QoS requirements represented by weights over criteria, and transactional properties expressed as a risk level. The result of our algorithm is a CPN corresponding to a Transactional Composite WS whose WS components locally optimise the QoS. We present experimental results to study the performance and the efficiency of our selection algorithm compared with an exhaustive one. Keywords: WSs; web services; selection; automatic transactional composition; quality of service; CPN; coloured petri net. Copyright © 2011 Inderscience Enterprises Ltd.