مدل جریان کار سرویس وب بر اساس عامل همکاری بین سازمانی

The service-orientated computing paradigm is transforming traditional workflow management from a close and centralized control system into a worldwide dynamic business process. A complete workflow serving inter-enterprise collaboration should include both internal processes and ad hoc external processes. This paper presents an agent-based workflow model to address this challenge. In the proposed model, agent-based technology provides the workflow coordination at both inter- and intra-enterprise levels while Web service-based technology provides infrastructures for messaging, service description and workflow enactment. A proof-of-concept prototype system simulating the order entry, partner search and selection, and contracting in a virtual enterprise creation scenario is implemented to demonstrate the dynamic workflow definition and execution for inter-enterprise collaboration.

Workflow management systems provide the automation of business processes where a collection of tasks is organized between participants according to a set of defined rules to accomplish some business goals (WfMC). The traditional inter-enterprise workflow is related to EDI (Electronic Data Interchange) and recently ebXML (electronic business XML) (ebXML), which coordinates business partners with pre-defined terms and thus constructs a close and secure business community. However, due to the lack of flexible mechanisms to deal with real-life situations, such as fast changing customer requirements and enterprise goal shifts, a static workflow definition designed at build time is inflexible to meet the complex, dynamic situations that happen at run time such as partner search and selection, bid negotiation, and workflow re-configuration. In a dynamic, loosely coupled collaborative environment such as B2B or B2C, a flexible and adaptive inter-enterprise workflow is more suitable for those small and medium Internet-based business enterprises (Yan, Maamar, & Shen, 2001). For a flexible workflow, only a rough, role-based workflow pattern is defined at the beginning. The initial workflow needs to be specified or pre-processed until such a workflow pattern can be described by a clear and executable workflow definition. Web services (W3C) provide an industrial standard for deploying, publishing, discovering and invoking enterprise’s services. From its emergence, many specialists have predicted that Web services will revolutionize the distributed computing paradigm and it will make various kinds of e-business (e.g., inter-enterprise collaboration and ASP paradigms) a reality. BPEL4WS is such a workflow process language for providing a formal specification of business processes and business interaction protocols. It uses executable business process and abstract process to ensure that different business processes can understand one another in a Web services environment, and that they can realize a dynamic composition. However, to achieve the required dynamic composition of a workflow, BPEL4WS still falls in short of building a direct logical relationship between an abstract process definition and an executable process definition, except developers manually define such a relationship. Ontology and reasoning mechanisms must be added on top of BPEL4WS to describe the relationships between workflow components, such as tasks, services and resources, for automatic reasoning and interpretation of a dynamic workflow process. Thanks to the emergence of Semantic Web research and standardizing efforts, OWL (Web Ontology Language) (W3C) becomes a promising ontology representation language that combines the description logic, formal logic and Web service standards. On the other hand, as significant research work has proved that software agents can provide a flexible, reconfigurable and coordinated approach to enhance workflow management (Xu et al., 2003 and Yan et al., 2001), the merging of agents with workflow brings a promising result. An agent-based workflow can be considered as a workflow process that is planed, performed, communicated, and coordinated in a multi-agent environment, in which the workflow is decomposed into multi-level collaborative tasks and each task represents a logical piece of work that contributes to the process. This paper presents an agent-based workflow model by integrating software agents, Web services, and workflow ontology to support dynamic workflow definition and execution for inter-enterprise collaboration. The proposed workflow model should include both internal and external workflow processes for their strong coherence relations. The paper is organized as follows: Section 2 introduces Web services, workflow ontology, and agent technologies in workflow coordination; Section 3 proposes an agent-based workflow model; Section 4 presents the basic definition of workflow ontology and its reasoning; Section 5 describes a virtual enterprise creation case study; Section 6 depicts the implemented proof-of-concept prototype; finally, Section 7 provides a conclusion and discusses our future work.

Today, workflow management systems often face the problem of runtime process changes and we cannot expect a pre-assumed design solution to handle all these changes (van der Aalst, 1999). Thus, a dynamic workflow should provide two meanings of flexibility: design composition and runtime composition. Using the agent-based Web service workflow model proposed in this paper, the abstract workflow definition can be interpreted dynamically at run time through service agents’ negotiation. Web service workflow ontology is evolved task by task depending on changing situations of workflow execution. Therefore, the effectiveness of workflow process can be improved by the dynamic interpretation of process ontology, the flexibility of process composition, and the reusability of process description. In this paper, we also present a case study of inter-enterprise collaboration with a proof-of-concept prototype to simulate the order entry, partner search and selection, and contracting in a virtual enterprise creation scenario. Contract Net-based agent negotiation is the primary mechanism to assist the dynamic workflow instantiation and collaboration. The proposed approach is particularly suitable for integrating heterogeneous software and hardware systems existed within an enterprise or among collaborative enterprises. Our future research in this area would be in two directions: improving semantic integration approaches to address complex scenarios and developing practical applications with industrial partners.