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Robotics and Computer-Integrated Manufacturing 23 (2007) 315–325
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An agent-based service-oriented integration architecture forcollaborative intelligent manufacturing
Weiming Shena,�, Qi Haoa, Shuying Wanga, Yinsheng Lia,b, Hamada Ghenniwac
aIntegrated Manufacturing Technologies Institute, National Research Council Canada, 800 Collip Circle, London, Ont., Canada N6G 4X8bSoftware School, Fudan University, Shanghai, 200433 PR China
cDepartment of Electrical and Computer Engineering, University of Western Ontario, London, Ont. Canada. N6A 5B9
Abstract
The rapidly changing needs and opportunities of today’s global market require unprecedented levels of interoperability to integrate
diverse information systems to share knowledge and collaborate among organizations. The combination of Web services and software
agents provides a promising computing paradigm for efficient service selection and integration of inter-organizational business processes.
This paper proposes an agent-based service-oriented integration architecture to leverage manufacturing scheduling services on a network
of virtual enterprises. A unique property of this approach is that the scheduling process of an order is orchestrated on the Internet
through the negotiation among agent-based Web services. A software prototype system has been implemented for inter-enterprise
manufacturing resource sharing. It demonstrates how the proposed service-oriented integration architecture can be used to establish a
collaborative environment that provides dynamic resource scheduling services.
r 2006 Elsevier Ltd. All rights reserved.
Keywords: Enterprise collaboration; Virtual enterprise; Software agents; Web services; Service-oriented architecture
1. Introduction
The manufacturing enterprises of the 21st century arefacing an environment where markets are frequentlyshifting, new technologies are continuously emerging, andcompetition is globally increasing. The rapidly changingneeds and opportunities of today’s global market requireunprecedented levels of interoperability to integrate diverseinformation systems to share knowledge and collaborateamong organizations. Fully integrated enterprises are beingreplaced by business networks in which each participantprovides others with specialized services. Traditional ITinfrastructures in which applications were managed andowned by one enterprise are being switched to networks ofapplications owned and managed by many businesspartners. Through this revolution, the temporary allianceof enterprises (so-called Virtual Enterprise, or VE) as a
e front matter r 2006 Elsevier Ltd. All rights reserved.
im.2006.02.009
ing author. Tel.: +1519 430 7134; fax: +1 519 430 7064.
ess: [email protected] (W. Shen).
whole can be more robust and agile to the transient marketopportunities.Toward this direction, enterprises all realize the cost of
automating cross-organizational transactions is very high,especially for the dynamic VE processes automation. Inview of the fact that distributed organizations are generallymanaged using heterogeneous software systems running onheterogeneous computing environments, the recentlyemerged Web Services technology provides a higher-levelinteroperability for leveraging business activities across theWeb either within an enterprise or among collaboratingenterprises. Manufacturing firms have been putting theirefforts to provide practical access methods to their existinginformation systems by leveraging the Internet and Web.However, what they have done today always assumes acollaboration network under a pre-assumed agreement. Onthe other hand, pure Web-based technologies, includingWeb services, cannot fulfill the needs of VE applications,particularly in that: (1) the Web service discovery mechan-ism is not enough for driving VE creation at run time; (2)the Web service description is not enough for driving VE
ARTICLE IN PRESS
BusinessProcesses
Description
Quality ofService
Transportand
Encoding
SOAP (Logical Messaging)
XML, Encoding
SecurityReliable
Messaging
BPEL4WS
WSDL, Policy, UDDI, Inspection
Transactions
Coordination
Other protocolsOther Services
Fig. 1. Classification of Web services standards.
W. Shen et al. / Robotics and Computer-Integrated Manufacturing 23 (2007) 315–325316
services description that is semantically intensive; and (3)the Web services business processes description, orchestra-tion, and security have hardly reached a maturity forprocess automation [1,2].
Intelligent software agents, which have been applied toenterprise integration for wrapping legacy systems, notonly provide an approach for functional integration, butalso promote business intelligence and collaborationamong enterprises for their inherited characteristics ofcommunication, interaction, cooperation, pro-activeness,and autonomous intelligent decision making. We believethat the combination of Web services and software agentsprovides a promising computing paradigm for efficientservice selection and integration of inter-organizationalbusiness processes. This paper proposes an agent-basedservice-oriented integration architecture, wherein enter-prise Web services are dynamically orchestrated on theInternet using agent behaviors built in them. A prototypesystem is designed to demonstrate the VE creation processin response to a resource requirement order.
The rest of this paper is organized as follows: Section 2provides an introduction and analysis of Web services,software agents, and their applications to enterpriseintegration; Section 3 discusses the requirements of VEcollaboration faced by manufacturing enterprises andaddresses the integration of software agents and Webservices technologies; Section 4 presents an agent-basedservice-oriented system architecture for manufacturingenterprises collaboration; Section 5 describes a case studyon virtual enterprise creation in response to a customer’sorder; Section 6 depicts an implemented software proto-type for inter-enterprise manufacturing resource sharing;Section 7 concludes the paper with some perspectives.
2. Service-oriented computing and software agents
Service-oriented computing (SOC) is considered as a newcomputing paradigm after the object-oriented paradigm. Itutilizes services as fundamental elements for developingapplications/solutions. Services are autonomous platform-independent computational elements that can be described,published, discovered, orchestrated and programmed usingXML for the purpose of developing massively distributedinteroperable applications.
2.1. Service-oriented computing and Web services
Web services technology is part of the SOC paradigmand can be considered as an implementation of the SOCmodel. Web services are featured with application, plat-form and provider independence. They provide an appro-priate paradigm for building open large-scale applicationenvironments, such as supply chains. In such environ-ments, services are not treated as isolated and one-timeaffairs but rather as elements of an interactive, dynamicand collaborative architecture. Service collaboration withinor across environments is modeled in terms of supported
transactions or processes that are subject to norms orprotocols specified for certain business domains. Servicesare thereby orchestrated vertically within one environment,or horizontally across multiple environments. As a result,an individual environment streamlines services in terms ofinternal transactions while restrains its function scope to behighly specific to the targeted user group. Multipleenvironments collaborate in order to extend their businesschains. Web services have been supported by major ITvendors through their commercial platforms such asMicrosoft’s .NET [3] and SUN’s J2EE [4]. There are alsounderlying technologies behind the promoted businessinitiatives such as HP’s Adaptive Enterprise [5] and IBM’sOn-Demand e-Business [6].To support the SOC concepts, Web services must
provide standards-based definitions of an interoperabilitycommunication protocol, mechanisms for service descrip-tion and discovery, approaches for service composition andorchestration, as well as a basic set of mechanisms forquality of service. The first initiatives of Web services andtoday’s de-fasco standards include SOAP [7], WSDL [8]and UDDI [9]. These standards together provide an openXML-based mechanism for application interoperability,service description and service discovery. In recent years,the standardization initiatives have been very active in theWeb services community to push basic Web servicesmechanisms to business applications. Among them, mostnotably are the Business Process Execution Language forWeb Services (BPEL4WS) [10] and ebXML (ElectronicBusiness XML) [11] for service composition and orchestra-tion; WS-Transaction [12] and WS-Coordination [13] forservice processes interaction; and other special protocolsrelated to security, service quality and business policies,e.g., WS-Trust [14], WS-SecureConversation [15], WS-Security [16], WS-SecurityPolicy [17], WS-Policy [18], andWS-ReliableMessage [19]. Fig. 1 shows a classification ofthe Web services standards mentioned above. Note thatthis figure does not intend to show all available Webservices standards. In fact, more standards are still beingproposed and developed.J2EE and .NET are two widely accepted industrial
application development frameworks for Web services.
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They support Web services protocols such as UDDI,SOAP, WSDL and BPEL4WS. A number of integrateddevelopment platforms such as IBM’s WebSphere [20] andMicrosoft’s Visual Studio .NET [21] implement the twoframeworks. Web services have achieved a number ofsuccesses at the application level, especially in e-Businessapplications: several examples are listed for .NET basedWeb services [22]; Sun Microsystems has helped FordFinancial to design and build a platform infrastructurebased on the J2EE framework [23]; Amazon.com Inc. andGoogle have given developers and owners the ability tobuild applications and tools using their Web services APIs.
Web services have had quick evolution and broadacceptance. However, there are still a number of issuesthat limit the applications of Web services in industry.Current Web services technologies lack semantic descrip-tion and generic service model. Petrie et al. [1] also statesthat the standards such as UDDI and WSDL are far fromenough for automated service searching, discovery andcomposition. They discussed shortcomings of Web servicesstandards through some Web searching examples andreached the conclusion that these standards are in short ofsemantics to understand the terms in XML structure.Without a common semantic model, a service-orientedframework has no foundation to facilitate Web servicesimplementation. Current Web services technologies havenot incorporated enough semantics in their profile andrepresentation. For example, UDDI is a profile-basedprotocol for registration and search, and it only relies onpre-defined keywords. WSDL needs additional informa-tion for ad hoc and automatic discovery of services.BPEL4WS is capable of supporting runtime semanticsbased on its logical operations and representation. How-ever, BPEL4WS is not based on a formal semanticsdescription. In order to address this issue, several researchefforts have been devoted to bringing semantics into Webservices [2,24–26]. W3C’s answer is OWL [27] based onDAML+OIL [28]. W3C/DARPA DAML-S [29] (recentlybeing replaced by OWL-S) is another example of resultingsemantic Web services markup languages, though it couldbe too ‘‘heavyweight’’ to industrial applications. However,no methodologies of these semantic Web approaches havebeen developed yet, particularly, because they are based oncurrent UDDI’s T-Model mechanism, they can onlydescribes pre-conditions and effects of the whole Webservices, but not of the individual operations.
2.2. Software agents and enterprise integration
Under the context of this paper, we view an ‘‘agent’’ as ametaphorical conceptualization tool at a high level ofabstraction (knowledge level) that captures, supports, andimplements features that are useful for distributed compu-tation in open environments. In our view, an agent is anindividual collection of primitive components that providea focused and cohesive set of capabilities.
The basic components of an agent usually includeproblem-solving, interaction, and communication compo-nents. A particular arrangement (or instance) derived bybasic agent components reflects the pattern of the agent’smental state as well as its reasoning rationale for achievingits goals. In a distributed context, e.g., collaborativemanufacturing, such agents play different roles (or providedifferent services) and are able to coordinate, cooperateand possibly compete with other agents including humanbeings. Significant efforts in software agents have yieldedwell-developed agent models and interaction protocols.The foundation for intelligent physical agents (FIPA) [30]has been focusing on developing specifications for agentcommunication, interaction and management.Many researchers have been probing into agent-based
solutions for enterprise integration and some reached theconclusion that the agent technology provides a naturalway to realize enterprise integration effectively. Agent-based enterprise integration has been a very active researcharea during the past ten years. In addition to significantacademic researches, some projects have attracted activeindustrial participation and developed industrial applica-tions [31–33]. In most projects, software agents are used toencapsulate existing legacy software systems using variousmiddleware approaches [34,35]. A detailed review onapplications of agent technology to manufacturing ingeneral can be found in [36].However, most of the above mentioned agent-based
approaches for business integration across or withinenterprise boundaries are demonstrated only throughexperiments or prototypes developed in research labs usingproprietary agent technologies. Generally speaking, unlikeWeb and Web services technologies, there is a lack ofindustrial support on the development and deployment ofpractical agent applications.
3. Integration of web services and software agents
A major objective of the Web services paradigm is tosupport enterprise collaboration to reach a higher level ofdistributed and reconfigurable business integration. Cur-rent efforts have been focused on Web services choreo-graphy and orchestration. The applied approaches, such asWS-Transaction and BPEL4WS, are mainly originatedfrom traditional top-down workflow principles, where Webservices are not treated as autonomous entities. However,the top-down ethics of the Web services business orches-tration has the following limitations, in the same way asother kinds of workflow based business process manage-ment approaches:
�
Dynamic business formation and effective selection ofservices. A coalition of collaborating enterprises (i.e., avirtual enterprise or VE) is generated by a collection ofselected Web services. Web services are created ‘‘on thefly’’ and it may be beyond human capabilities to analyzethe required services and select them manually. A kind
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of brokering service provided by agent technologies isrequired for the creation and operation of a virtualenterprise.
� Service dynamic composition. Once the participants andtheir services are confirmed to join a VE, the services arerequired to be compiled dynamically according topredefined abstract business rules so that a businessprocess can be carried out upon the VE. For example, inan ordering process, the generic workflow can bedescribed as receiving an order, composition of a VEto satisfy the order, contract generation, and contractconfirmation. The fixed pattern of business processesdescribed by BPEL4WS cannot meet the requirementsof collaborative manufacturing, where dynamic con-sortiums of manufacturing enterprises are formed ‘‘onthe fly’’ by negotiations or trust in order to catch thetransient market opportunities.
� Flexible cooperation strategies. The dynamic character-istics of business collaboration generally require theintroduction of flexible cooperation strategies in theconsortium formation processes, moreover, in thecoordination of operations of a formed consortium,and the re-negotiation processes to adjust a currentconsortium under certain circumstances. The behaviorsrevealed by the defined business workflow can bepredicted because of the explicit descriptions of roles,nodes (services), control patterns (service sequences andcontrol logics), invocation interfaces (WSDL descrip-tions), and the data transferring among services.
� Semantic and ontology problem. Resulting from theuncertainties of the dynamic enterprise collaboration,semantic and ontology problem in service orchestrationis inevitable. This problem is proposed by someresearchers in inter-enterprise business workflow initia-tives [37–39]. However, more complicated situationsarise with the introduction of flexible participants andflexible cooperation strategies into a cooperation pro-cess. According to our knowledge, none of the currentworkflow patterns or Web service process flow definitionlanguages is able to handle such complex situations.Semantic and ontology in workflow has to be enrichedor evolved because data exchange, information flow aswell as logistics are more critical factors to practicalbusiness integration than the workflow description andworkflow engine itself.
Software agents have been proved to handle sophisti-cated interaction patterns. Agent-orientation is an appro-priate design paradigm to enable automatic and dynamiccollaborations, especially for e-Business systems withcomplex and distributed transactions. In services realiza-tion, software agents are very essential for the provision ofa focused and cohesive set of active capabilities. Therefore,we envisage a combination of agent and Web servicestechnologies and strongly believe that we are on the righttrack towards an evolution of current SOC paradigm.Software agents can be one of the essential evolvements of
Web services in that they are functional entities, instead ofsimple interaction delegations or communication proxies.The idea is to exploit agents’ capabilities of proactiveinteractions to enhance Web services’ behaviors. With sucha computing paradigm, software components, each repre-senting both a service and an agent, cooperatively orcompetitively interact to provide unified services in aspecified environment, such as brokering, pricing andnegotiation in an e-marketplace, as well as cross-enterpriseenvironments, such as integration and cooperation in avirtual enterprise. This is aligned well with Huhns andSingh’s prediction [37] ‘‘agents will become an essential part
of most Web-based applications, serving as the ‘glue’ that
makes a system as large as the Web manageable and viable.’’The purpose of the combination solution is to integrate
software agents and Web services technologies into acohesive entity that attempts to avoid the weaknesses ofeach individual technology, while reinforcing their indivi-dual strengths [24]. The merging of service-oriented andagent-based approaches has been a hot topic of research inrecent years. Petrie et al. [1] discussed the shortcomings ofWeb services standards and how logical AI techniques likedeclarative commands, agents, and planning can be used toaddress some of these shortcomings. They proposed a FX-Agent approach to address Web services discovery andcomposition of Web services. Matskin et al. [40] identifiedWeb services composition as an important issue forefficient selection and integration of inter-organizationaland heterogeneous services on the Web and they believedthat software agents can help make Web services ‘‘pro-active’’. In their system, provider’s Web services arewrapped into individual providers’ agents on an agent-based marketplace providing services for customers’agents. Maamar et al. [41] presented an agent-based andcontext-oriented approach that supports the compositionof Web services. During service composition process,software agents engage in conversations with their peersto agree on the Web services that participate in thisprocess. Liu et al. [42] proposed a conceptual model ofagent-mediated Web services for intelligent service match-making. In fact, most of research efforts in the literaturelike above mentioned approaches can be roughly categor-ized in to ‘‘agentification’’ of Web services into an agentcommunity. We proposed a different approach for agentand Web services integration [24]. In our agent-based Webservices (AWS) framework, an agent core is built into eachWeb service, so that a Web service is itself an agent. Nomatter the agentification of Web services as agents in amulti-agent system [41] or encapsulation of agents as Webservices over the Internet [24], both approaches share thecommon goal that, by taking the advantages of Webservices and agents, the resultant integrated solution willproduce a sophisticated paradigm for Internet computing.There is an interesting industrial movement toward
this direction, as reported in a recent technical reporton Web service architecture [43]. W3C introduced asimilar concept, where software agents are treated as the
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foundation for Web services architecture. In this model,software agents are not used for service communicationfront ends or as proxies, rather, they are treated as basicentities that encapsulate Web services—‘‘A Web service is
an abstract notion that must be implemented by a concrete
agent.’’ Agent orientation for software construction andsemantics-based interaction can be effectively applied forWeb services applications. However, the definition of anagent by W3C under the context of Web ServicesArchitecture is a specialization of the definition inarchitecture of the Web: ‘‘an agent is a program acting on
behalf of a person or an organization.’’
4. An agent-based service-oriented integration architecture
We envision a Web service-based environment as acollection of economically motivated agent-based Webservices. Software agents are dynamically implemented asservices with different functionalities and roles. In fact, thedynamic agent-based behavior model plus the Web service-based interoperable protocols can generate a flexible,reconfigurable and coordinated approach to performbusiness process management both across enterprises andwithin an enterprise.
The agent-based service-oriented architecture for manu-facturing enterprise collaboration is illustrated in Fig. 2. Inthis system, each enterprise provides a number of Webservices registered in the UDDI repository. The Webservices are implemented by the AWS [24] technology witha built-in agent core. So, enterprises are given the ability to
Fig. 2. The agent-based service-oriented system
negotiate bids with upper mediating agents. Moreover,upper mediating agents are also implemented as a networkof AWS on the Internet. The integration of software agentsand Web services can be proposed at both the design leveland the implementation level. At the design level, weencapsulate Web services as agent models so that eachagent functions on behalf of a Web service in its action andrelation to the environment. In this sense, we can treat aWeb service as a semi-autonomous agent. On the otherhand, Web services can be used to describe the externalbehaviors of software agents. Therefore, agents can beused to build high-level models with flexible interactionpatterns, while Web services are more suitable for solvinginteroperability problem of various applications in realimplementations. At the implementation level, UDDI,WSDL and SOAP provide such capacities as discovery,deployment and communication, while specifications suchas BPEL4WS provide service composition and processenactment.Major components of the proposed system are described
as follows:
�
ar
Web portal is a Web interface that is designed for usersto access and manage related information. From theWeb portal, the customers register their profiles, placeorders, select bids, and manage the contract informa-tion.
� Workflow planner is a software agent that is responsiblefor coordinating the workflow process. The workflowplanner includes a workflow engine. When a workflowprocess is triggered, the workflow planner selects a
chitecture for enterprise collaboration.
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related workflow definition from process definitionrepository. According to the defined relations andproperties, the workflow engine within the workflowplanner finds an execution task and then sends it to thebroker agent for task allocation.
� Broker agent plays an important role in coordinating theAWS. In our system, the broker agent performs fouractions: order generation, partner filtering, bid negotia-tion, and contracting. As shown in Fig. 2, after the orderis submitted, the broker agent needs to query theworkflow planner for an execution task and then askontology agent for a list of related supplier agents toexecute the task.
� Supplier agent is an agent on behalf of an enterprise thathas capabilities of providing certain services such asmanufacturing, shipment or payment. A supplier agentregisters its services to the UDDI registry, receives thetask execution request from the broker agent, schedulestasks using its internal agent-based scheduling systemand fulfills the contract after the customer makes thedecision.
� UDDI is a static repository that provides suppliers’information with standard terms that contains enter-prise’s businesses, capabilities, relationships and con-straints.
� Ontology agent provides semantic integration services,responds to service queries and performs ontologyreasoning and match-making. In order for the ontologyagent to compare the requested capabilities with theadvertised capabilities (by supplier agents), the re-quested and advertised capabilities must be formulatedin a way that they are comparable in terms of serviceperformance. In our system, when the broker agentsubmits a service query to the ontology agent, theontology agent will check first its local service ontologyrepository then the UDDI registry, find the matching
Enterprise’s
Database Database
ResourceAgent 1
MediatorAgent
InterfaceAgent
ResourceAgent 2
Fig. 3. Agent-based scheduling
services, and return this matching list to the brokeragent. An ontology agent may have advanced learningabilities in order to gather non-functional informationof services on the fly, such as QoS (Quality of Service).
� Interface agent performs functions as an applicationgateway that is a joint point of the inter-enterprisesystem and the intra-enterprise system. Its functionsinclude transferring messages, receiving tasks, returningorder bids, and controlling access security. When thesupplier’s Web service receives a message, it is trans-ferred to the interface agent first. The content of SOAPmessage is deprived, checked and directed to theresponsible agent.
� Mediator agent is a coordination agent at the enterpriselevel that communicates with resource agents to performtask scheduling, task execution and execution processmonitoring. As shown in Fig. 3, when an order isreceived, the mediator agent decomposes it as a set oftasks and finds possible resource agents to completethese tasks. The resource scheduling is a negotiationprocess in that the mediator agent sends the bid requestto resource agents and makes the decision after receivingthe bid results.
� Resource agents represent enterprise’s internal re-sources such as legacy systems, software, machines,and workers. Each resource agent is on behalf ofone resource. When a resource agent receives a call-for-bid from a mediator agent, it will prepare a bidaccording to its knowledge (including its capability,schedule, status, and cost) and send a bid. Once the bidit proposes is awarded, the resource agent will commit tothe task by fixing its schedule and prepare for taskexecution.
� Directory Facilitator (DF) has the registrationservice functionalities for other agents in the internalagent-based manufacturing scheduling system, keeps
Web Service
Database
DFAgent
ResourceAgent n
within an enterprise.
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up-to-date agent registration, informs all registeredagents with updated registry, and provides look-upand matchmaking services to other agents within theinternal scheduling system.
As shown in Figs. 2 and 3, the proposed systemarchitecture is composed at two levels. At the inter-enterprise level, communication among agents is basedon Web services standards and several Agent-based WebServices are proposed such as workflow planner, brokeragent, ontology agent and supplier agents, as well as twoother software entities (not agents): Web portal and UDDIregistry. At the enterprise level, there is a FIPA-compliantmulti-agent system composed of a directory facilitator, aninterface agent, a mediator agent, and several resourceagents. The FIPA Contract Net protocol [30] is used bothat the inter-enterprise collaboration level for the selectionof service providers and at the enterprise level for theallocation of manufacturing resources (see Fig. 3). OtherWeb services standards such as BPEL4WS will be adoptedfor further interactions/collaborations between businesspartners.
5. Case study of inter-enterprise resource sharing
We choose the inter-enterprise resource sharing [44] asour case study to demonstrate the proposed agent-basedservice-oriented architecture for enterprise collaboration.In this case study, each enterprise is encapsulated as anindividual Web service on the Internet and it owns anumber of expensive manufacturing resources that can beshared with other enterprises. A software prototype system(described in detail in the next section) has beenimplemented to demonstrate how manufacturing enter-prises can dynamically establish a virtual enterprise inresponse to a customer’s requests. The reasons why wechoose to demonstrate this problem are based on thefollowing observations:
�
SMEs need to have focused competencies. � Each of them owns a number of expensive manufactur-ing resources.
� SMEs would like to join a consortium in order tomaximize their profit margins by increasing resourceutilization as much as possible.
� An SME usually has limited funds and has to be verycareful on investing in expensive manufacturing equip-ment.
� SMEs specially need to cooperate so that they togetheras a virtual enterprise can be competitive on businessopportunities.
� All SMEs are concerned with whether their proprietaryinformation can be protected when collaborating withother companies over the Internet.
� The identity and integrity of an SME congregation canbe recognized through the virtual world.
process) is a composite business process that is made updynamically by a set of individual services, workflow and
Since the creation of a VE (during a customer’s ordering
ontology issues must be considered in implementation. Weaddressed these issues in details in a separate paper [45]through a layered agent-based workflow concept, workflowontology and ontology reasoning mechanism. Here, majoractivities in the workflow are briefly presented for a betterunderstanding of the case study.
Service ordering: The user places an order through aWeb portal. A service order process is separated as asequence of order input, order generation, and ordersubmission. Once the order is submitted, for eachindividual order, the broker agent needs to query theworkflow planner for task decomposition and workflowinstantiation. The workflow planner agent makes itsdecision by workflow ontology reasoning from the abstractworkflow definition to the executable workflow definition.When the broker agent gets an execution task, it tries tofind a service agent to execute the task.
Partner search: The search and selection of businesspartners is a critical step in the formation of a virtualenterprise. Partner search can be done based on followingresources: (1) private information resources such as thelocal service registration list of the broker agent; (2)ontology service registry at the ontology agent site; and (3)public service registry such as a public UDDI repository. Infact, the partner search process is carried out by the brokeragent through checking sequentially the above threeresources with decreased priorities. The partner searchresult is a list of matching service agents that best serve theaccomplishment of the identified task.
Bidding process: After the broker agent recognizes thepotential service agents, it needs to negotiate with them forcost estimation, production planning, and conflict resolu-tion. The CNP (Contract Net Protocol) [46], commonlyused as an interaction protocol in a multi-agent commu-nity, is adopted for this inter-enterprise negotiationprocess. A ‘‘Call-for-Bid’’ message initialized by the brokeragent is encoded using SOAP denotations and sent to allpotential service agents. Each service agent is required toreturn a ‘‘Bid’’ to the broker agent. The broker thencollects the return bids and feeds back related informationto the customer.
Partner selection: The decision of partner selection ismade by the broker agent (in the case of an automaticsystem) or the customer (in the case of an interactivesystem) after collecting all possible bids and checkingwith its decision rules. The most promising alternativefor virtual enterprise partnership configuration is chosenbased on the service time, cost, quality, trust, and otherfactors.
Contracting: Contracting process is used to achieve abusiness agreement between the customer and the servicesuppliers. A contract is generated by the broker agent mainlybased on customer’s order, payment and shipping informa-tion as well as suppliers’ bid information. The customer
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keeps the contract and its copies are sent to the selectedservice agents (participant enterprises) for execution.
6. Prototype implementation
The Web portals and Web services are developed by JavaWeb Services Development Pack (JWSDP) [47]. TheJWSDP provides a convenient all-in-one package fordevelopers who want to start building and deployingapplication Web services quickly.
In the implemented prototype, we assume three enter-prises (A, B, and C) participating in the virtual enterprisewishing to offer services to share their manufacturingresources, say CNC, EDM or CMM machines. Eachenterprise’s resource scheduling service is encapsulated inan individual agent-based Web service (AWS) on theInternet. Enterprise resource scheduling AWSs are pub-lished to a shared UDDI server. The broker agent mayquery the UDDI for a list of enterprises and do simplesemantic matchmaking based on the resource capacitiesthat an enterprise published in the UDDI.
A Web portal is developed to connect all enterprisesrepresented by their Web services. For simplicity ofimplementation, functions of the workflow planner agentare combined into the broker agent. The user places anorder through the Web portal (Fig. 4). The broker agent,
Fig. 4. Snapshot of the ord
which is implemented also as a run-time workflow engine,has the functions of service discovery, coordination andmediation. The broker agent contacts the ontology agent toget a list of potential supplier agents. Then the broker sendsout a ‘‘Call for Bid’’ to the potential supplier agents andsince then, a collaboration/negotiation process based onthe Contract Net Protocol is initiated and carried outbetween the broker agent and three enterprise Webservices. Each enterprise will submit a bid if its dynamicscheduling service is able to allocate necessary manufactur-ing resources to meet the requirements of the customer. Asa result, a list of bids proposed by enterprises is fed back tothe customer for decision making (Fig. 5). However, thedecision of bid selection and order contracting depends onthe choice made by the customer in the current implemen-tation.After the user makes his decisions on partner’s selection,
the broker dynamically builds up an executable processflow for order enactment. Finally, a contract is generatedby the broker agent and its copies are sent to the selectedenterprise(s).For each enterprise to respond to the ‘‘Call for Bid’’
from the broker with a bid, an agent-based manufacturingscheduling system (as shown in Fig. 3) is implementedbehind the enterprise AWS for dynamic scheduling ofmanufacturing resources (those expensive machines only).
er entry user interface.
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Fig. 5. Snapshot of the bid selection interface.
Fig. 6. Snapshot of agent-based scheduling system (within an enterprise).
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A number of agents are implemented for manufacturingresources’ dynamic scheduling including: a DF (DirectoryFacilitator) agent for machine agents’ registration, aninterface agent for connecting this agent-based manufac-turing scheduling system to the enterprise’s AWS, and ascheduling mediator agent for scheduling coordinationwithin the enterprise.
AADE (Autonomous Agent Development Environ-ment), a FIPA compliant engineering-oriented agentframework developed at the National Research CouncilCanada’s Integrated Manufacturing Technologies Institute[48], has been used for the implementation of agent-based dynamic manufacturing scheduling system at theenterprise level, where each machine is represented byone resource agent (machine agent). A screenshot for theagent-based manufacturing scheduling system runningbehind an enterprise’s Web service is shown in Fig. 6.Communication among agents on both the inter-enterpriseand intra-enterprise levels is implemented based on FIPAACL [30].
7. Conclusions and perspectives
Service orientation is an emerging computing paradigmwith new standards and tools being proposed anddeveloped by industrial IT leaders. Software agents havebeen studied for about two decades, but most of R&Dwork has been done within the academic community andhas not been widely applied in industry. Integratingsoftware agent technologies with service-oriented comput-ing provides a promising solution for cooperative dis-tributed systems integration, and particularly for nextgeneration collaborative manufacturing systems.
This paper presents an agent-based service-orientedsystem architecture for manufacturing enterprise colla-boration or collaborative intelligent manufacturing ingeneral. It provides a unified framework to integratesoftware agents and Web services, and supports sophisti-cated dynamic and automatic services collaboration formanufacturing enterprises. Due to its generic nature, theproposed architecture can also be applied to other e-Business applications.
The prototype system presented in this paper has beendemonstrated to local small and medium-sized enterprisesand is believed to be practical and useful in industry.Further development and improvement of the system isunderway for possible commercial uses in a near future.
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