Web Service Discovery and Composition using the Web Service Integration Gateway Dominic Greenwood Whitestein Technologies AG
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Paul Buhler College of Charleston
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Alois Reitbauer Profactor Research GmbH
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1. Introduction In recent years Web services and their associated standards have received an enormous amount of attention. Web services hold the promise of creating a distributed global repository of network addressable units of computation. This repository will undoubtedly generate a disruptive force that will fundamentally change not only the methodologies and techniques used for software construction, but will even challenge our perception of what constitutes a software application. In the future software applications will be increasingly amorphous, dynamically adapting their composition at run-time in response to changes in environmental context and conditions. With this vision in mind, the authors welcome the EEE-05 Challenge competition, which in its inaugural year is focused on Web service discovery and composition. This short paper introduces our ideas concerning the design of an efficient and robust solution to the issued challenge. Our strategy centers on the use of the Web Services Integration Gateway (WSIG) [1], which as depicted in Figure 1, enables transparent, bi-directional interaction between Web services and software agents. Although we recognize that the ultimate winner of the EEE-05 Challenge will likely employ brute-force techniques; we believe that our approach will acutely illustrate the expressive power of semantic reasoning for the composition of Web services. Collectively, the authors believe that we are entering a new era of computing enabled in part through a union of the two complementary paradigms: service-oriented and agent-based computation. Web services are the computational resources with agents providing a coordination framework [2]. This argument is strengthened through statements defining this relationship made in the W3C Web Services Architecture Working Group Note [3]. It is our objective to illustrate the utility and power of the WSIG for JADE [4] as a means to discover and compose Web services. A conceptual overview of the WSIG is depicted in Figure 1.
Figure 1. The architecture of the WSIG
2. Technical Description The competition entry will consist of a JADE 3.31 platform, deployed with a standard configuration other than the addition of the WSIG and associated support software, including an Axis web server and UDDI registry running as JADE services. The competition entry will be driven by a JADE application consisting of a number of agents acting in concert to optimize the Web service discovery and composition process, which will execute in three phases: Registration, Discovery and Composition.
2.1. Registration During the registration phase, the supplied Web service descriptions will be processed. This is likely to consist of the following steps: (1) WSDL entries will be loaded into the WSIG UDDI repository. (2) WSDL descriptions will be automatically translated into ACL/OWL2 by the WSIG Service Description 1 JADE 3.3 is planned for release in early 2005. 2 FIPA-ACL is the Agent Communication Language used by JADE. OWL is the Ontology Web Language from the W3C.
Proceedings of the 2005 IEEE International Conference on e-Technology, e-Commerce and e-Service (EEE’05) 0-7695-2274-2/05 $ 20.00 IEEE
Translator. (3) ACL/OWL service descriptions will be automatically registered in the JADE Directory Facilitator (DF).
2.2. Discovery The discovery phase requires the demonstration of efficient and robust service matching capabilities for a specific discovery request, or set of requests. Based on an incoming discovery request a JADE agent will be launched to perform the discovery, identifying full and partial matches for the required Web service descriptions on the platform DF. This is likely to consist of the following steps: (1) Launch of JADE Discovery Agent (DA) that will manage the WS discovery (2) Issue a FIPA-Request message from the DA to the JADE Platform DF with search criteria matching the specified service requirements (3) Complete and partial matches will be handled seamlessly by the DA
2.3. Composition Our approach to the composition phase is designed to demonstrate the utility of an agent-based. The basis for the challenge is that the software infrastructure should be able to compose services on-the-fly in response to a discovery request that can not be satisfied by a single, atomic service. The composition objective is hence to achieve a 'complex requirement' which implies finding the 'leastcost' composition of Web services that achieves some objective function. We view this as a backwards-chaining optimization problem that takes the objective as an input and determines the collection of Web service compositions that satisfies that objective. The compositions will be terminated when either the inputs of the current 'lowest level' of Web services cannot be satisfied by the outputs of other registered Web services, or when the 'cost' of the composition exceeds one that has already been calculated. The 'cost-function' is to be decided, but is likely to be uniform and consist of the least-number of services required to fulfill the objective taking into account processing time and accuracy of result. A key aspect of the composition process is that it will explore the search space of Web service interconnections in parallel by distributing the effort across several agents. Composition requests will be processed as follows: (1) Launch of a JADE agent, nominally called the Composition Controller Agent (CCA), which will be provided the composition requirements specified by the competition organizers in a pre-formatted representation.
(2) A CCA behavior is then initiated that searches the platform DF for Web service descriptions that match (full or partially) the required objective of the composition. This "output endpoint" may only be achieved through a conjunction of Web services with outputs for which no other Web service can be found with matching inputs. As such, the 'starting point' for the search will consist of the inputs to this single or conjunction of discovered Web service descriptions. (3) If a single "output endpoint" is found the CCA searches for those Web services with outputs matching the inputs required by the "output endpoint" Web service. (4) A Composition Search Agent (CSA) is launched for each Web service identified as either being an "output endpoint" or, in the case of a single "output endpoint", as a first level contributor to the final output. Each CSA is then responsible for backtracking through the composition from that starting point to determine a solution path. Current results are periodically sent back to the CCA for collation. We are currently examining the PROSA framework [5] as a means of coordinating the activities of the CSAs. The PROSA framework is based upon a holonic architecture. Holonic approaches are recursively decomposable and would make the distinction between CCA and CSA a matter of perspective. A CSA may play the role of a CCA to other CSAs that have been launched to explore a subset of the search space. We believe that this flexibility will enable more local control that can be exploited to enhance coordination and cooperation amongst the agents. (5) The CCA collates information from each CSA and publishes the composition results.
3. References [1]
[2]
[3] [4] [5]
D. Greenwood and M. Calisti, "Engineering Web Service - Agent Integration," in IEEE Conference of Systems, Man and Cybernetics, The Hague, 2004. P. Buhler and J. M. Vidal, "Towards adaptive workflow enactment using multiagent systems," Information Technology and Management Journal: Special Issue on Universal Enterprise Integration, vol. 6, pp. 61-87, 2005. W3C Web Services Architecture Working Group Note, Feb 2004, http://www.w3.org/TR/ws-arch/ JADE, The Java Agent Development Framework, http://jade.tilab.com/ H. V. Brussel, J. Wyns, P. Valckenaers, L. Bongaerts, and P. Peeters, "Reference architecture for holonic manufacturing systems: PROSA," Journal of Manufacturing Systems, vol. 37, pp. 255274, 1998.
Proceedings of the 2005 IEEE International Conference on e-Technology, e-Commerce and e-Service (EEE’05) 0-7695-2274-2/05 $ 20.00 IEEE
