Web Coordination Bonds: A Simple Enhancement to Web Services Infrastructure for Effective Collaboration Sushil K. Prasad and Janaka Balasooriya Computer Science Department Georgia State University sprasad@gsu.edu Abstract The Web Services need to extend beyond the basic service architecture (invoke and respond) to self- coordinating Web processes collaborating among themselves in the desired configuration as per user’s application (transient to long lasting). A core set of artifacts are needed to allow these Web processes to hook together in a desired structure to enforce automatic information flow, group constraint satisfaction, and data and control dependencies, all without any central coordinating authority. We propose Web Coordination Bonds, analogous to the chemical bonds, as a set of such core artifacts for effective collaboration among Web Services. There are two types of Web bonds: subscription bonds allow information, control and event flows whereas negotiation bonds enforce dependencies and contracts. Web bonds are simple yet powerful, and we demonstrate how they can be employed to create (model) and enforce (deploy and execute) producer- consumer and shared-resource relationships, workflow scenarios, and atomic transactions. We have developed and prototyped a middleware called System on Devices (SyD) incorporating Web bonds, and have employed it to prototype a few distributed applications which bond existing Web Services together to collaborate. Much remains to be done, including theoretical treatment of Web coordination bonds. 1. Introduction We aim to develop a few core artifacts for effective coordination/collaboration among Web entities. A good analogy would be the molecular bonds in chemical compounds, which are too simple yet extremely powerful to enable all sorts of basic and complex chemical compounds to exist naturally and to be manufactured artificially. Different atoms expose sites with certain number of either excess or shortage of electrons. For example, oxygen atom has two negatively charged sites, and hydrogen has a deficit of one electron, giving it a positively charged site. To form water molecule, therefore, two hydrogen atoms bond with an oxygen atom - each bond is just a sharing of an electron between a donor and a recipient site. The Web Services are simple or composite server objects situated on the Web with well-defined interfaces and are the “Web atoms.” Molecules are, therefore, analogous to all collaborating processes involving individual Web Service components. The list of such “Web molecules” spans transient to long running collaborative processes - transactions, client-server and p2p distributed applications, workflows as well as virtual organizations. Taking the analogy further, the challenge is to (i) define the analogous “bonding sites” or simple “Web hooks” in the Web Service interface needed to mesh multiple Web entities together, and (ii) develop the analogous concept of a few simple yet powerful types of “Web bonds” which would be the coordination threads to bind and produce the “Web molecules” out of multiple “Web atoms.” These “Web bond” artifacts should allow rapid modeling and deployment of collaborative applications of all kinds and complexities. As things stand today, the hooks exposed by the Web Services are the basic methods published and the bonds available are no more capable than the one-time invocations of those methods by a client Web entity. Section 5 contains discussion on relevant technologies to enhance the threading/gluing of Web Services for transactions, workflows, etc. However, much remains to be done in terms of extracting the simple core bonding artifacts which are necessary and sufficient, or to prove that such an exercise in itself is flawed. This paper is a proposal for Web coordination bonds (also alternatively called Web bonds or coordination bonds, for short, or coordination bonds to generalize to Web and non-Web entities) as one such set of core artifacts for Web Service coordination/ Proceedings of the 37th Hawaii International Conference on System Sciences - 2004 0-7695-2056-1/04 $17.00 (C) 2004 IEEE 1