The development of new services through the integration of existing ones has gained a considerable momentum as a means to create and streamline business-to-business collaborations. Unfortunately, as Web services are often autonomous and heterogeneous entities, connecting and coordinating them in order to build integrated services is a delicate and time-consuming task. In this paper, we describe the design and implementation of a system through which existing Web services can be declaratively composed, and the resulting composite services can be executed following a peer-to-peer paradigm, within a dynamic environment. This system provides tools for specifying composite services through statecharts, data conversion rules, and provider selection policies. These specifications are then translated into XML documents that can be interpreted by peer-to-peer inter-connected software components, in order to provision the composite service without requiring a central authority.of Web services. In this paper, we distinguish the following key issues when composing and executing Web services:Fast composition: The "why" part of Web services composition is now widely understood [13,11]. However, the technology (i.e, the "how" part) to compose and execute Web services in appropriate time-frame, has not kept pace with the rapid growth and volatility of available opportunities. Indeed, the development of integrated Web services is still largely ad-hoc, timeconsuming and requiring a considerable effort of lowlevel programming. This approach is clearly tedious and hardly scalable because of the volatility and size of the Web. The need for fast composition and deployment of Web services, will require a high-level declarative service composition language.
Scalable composition:The number of services to be integrated may be large. Consequently, approaches where the development of an integrated service requires the understanding of each of the underlying services are inappropriate. In addition, Web services may need to be composed as part of a short term partnership, and then disbanded when the partnership is no longer profitable. This form of partnership does not assume any a priori defined relationships between services. Thus, the integration of a large number of dynamic Web services, requires scalable and flexible techniques.
Distributed execution:The execution of a composite service in existing techniques is usually centralised, whereas the participating services are distributed and autonomous. A centralised execution model incurs sever problems including, scalability, availability, and security problems [5]. Given the highly dynamic and distributed nature of Web services, we believe that novel techniques involving peer-to-peer execution of services will become increasingly attractive. Peer-topeer computing is gaining a considerable momentum,
