The increasing demand of services delivery in existing heterogeneous e-learning systems is a hot research issue. In order to enable the interoperability, we propose a solution based on cloud computing technology for instant building and delivering new services composed of existing web services discovered through UDDI or web services marketplace. In this paper, we present our approach to solve integration problems between heterogeneous e-learning systems. A larger variety of e-learning providers and requesters will be connected through a broker. Then, we expose our research in modeling services composition with a support of quality of service properties. Thus a model based on extension of Petri-nets aims to transform the operational semantics of service composition framework. In fact, this paper suggests this model to the analysis of web services composition in order fully match different users' request.