  Nowadays, with the emergence and the evolution of new technologies, such as
e-business, a large number of companies are connected to Internet, and have
proposed web services to trade. Web services as presented, are conceptually
limited components to relatively simple functionalities. Generally, a single
service does not satisfy the users needs that are more and more complex.
Therefore, services must be made able to be composed to offer added value
services. In this paper, a web services composition approach, modelled by
Objects-Oriented Petri nets, is presented. In his context, an expressive
algebra, which successfully solves the web services complex composition
problem, is proposed. A java tool that allows automating this approach; based
on a definite algebra and a G-nets meta-model, proposed by us, is developed.
