Aberer, Karl

Klingemann, Justus

Wäsch, Jürgen

Infoscience - École polytechnique fédérale de Lausanne

Adaptive Outsourcing inCross-Organizational WorkowsJustus Klingemann, Jurgen Wasch, and Karl AbererIntegrated Publication and Information Systems Institute (GMD-IPSI)GMD { German National Research Center for Information TechnologyDolivostr. 15, D-64293 Darmstadt, Germanyfklingem,waesch,abererg@darmstadt.gmd.dehttp://www.darmstadt.gmd.de/~fklingem,waesch,aberergProceedings of the 11th International Conference on Advanced Information Sys-tems Engineering (CAiSE'99), Heidelberg, Germany, June 1999, pp. 417-421.Adaptive Outsourcing inCross-Organizational Workows?Justus Klingemann, Jurgen Wasch, and Karl AbererGerman National Research Center for Information Technology (GMD)Integrated Publication and Information Systems Institute (GMD-IPSI)Dolivostrae 15, D-64293 Darmstadt, Germanyfklingem,waesch,abererg@darmstadt.gmd.deAbstract. The workow concept has been very successful in streamlin-ing business processes by automating the coordination of activities, buthas so far been limited to the use within single organizations. Any at-tempt to distribute workows among dierent organizations has to facethe problems posed by the complex relationship among autonomous or-ganizations and their services. To address these problems we propose aservice-oriented model for cross-organizational workows. Modeling theworkow execution as a cooperation of services allows dierent orga-nizations to interact via well-dened interfaces. We further show howthe execution can be optimized by selecting services depending on theircontribution to quality criteria of the workow.1 IntroductionCompetitive markets force companies to minimize their costs while at the sametime oering solutions which are tailored to the needs of their customers. Thisurges organizations to form virtual enterprises by outsourcing activities to ex-ternal service providers. Hence, business links with other organizations have tobe set up and managed. This has to be achieved in a fast and exible way toguarantee a short time to market while allowing a dynamic reaction to new cus-tomer demands and changing oers of service providers in electronic commerceenvironments.Information technology has provided dierent technologies to address theserequirements. The workow concept [1{5] has been very successful in coordinat-ing and streamlining business processes but is so far limited to a single organi-zation. On the other hand, the tremendous growth of global networks like theinternet provides the possibility to eciently exchange data and communicatewith a large number of possible service providers. Thus, workow managementsystems (WfMS) can limit their scope no longer to a single organization buthave to exploit the network infrastructure to cross organizational boundaries.However, the extension of workows beyond the borders of a single enter-prise raises new challenges. One important challenge is the necessity to choose?This work has been partially supported by the ESPRIT project CrossFlow(www.crossow.org). However, it represents the view of the authors.among dierent services that potentially satisfy the customers requirements. Inparticular, it has to be decided which activities or group of activities shouldbe outsourced to which business partners. Relevant criteria with regard to thatdecision are the required time, cost, or the adherence to domain-specic qualityof service parameters.The autonomy of the participating organizations implies that the initiatorof the workow has only limited control over the outsourced activities. Thisrequires that both sides agree on an interface which allows the service requesterto monitor and probably control the outsourced activities to a certain extent.To address these problems, we propose a service-oriented model for cross-organizational workows. Modeling the workow execution as a cooperation ofservices allows dierent organizations to interact via well-dened interfaces. Wefurther show how the execution can be optimized by selecting services dependingon their contribution to quality criteria of the workow.2 A Service-Oriented Model for Cross-OrganizationalWorkowsIn this section, we describe our conceptual model for cross-organizational work-ows. However, we conne ourselves to the essential concepts which are necessaryto understand the approach presented in this paper. For further details see [6].We consider a workow as a collection of activities which are related by certaindependencies. A workow is modeled as a graph with activities as nodes andedges which represent the control and data ow. In addition, quality of service(QoS) parameters are assigned to the workow, e.g., the maximal duration andthe maximal cost allowed for a workow. Despite these more or less application-independent QoS parameters, domain-specic QoS parameter can exist.In order to allow the execution of activities at runtime, we need to dene amechanism that assigns activities to particular \agents" that are responsible forthe execution of the activity instances. Usually, in intra-organizational workows,agents are considered to be human beings or computer programs. If a workowis allowed to span dierent organizations, there is a third kind of agents that canbe involved in the execution of a cross-organizational workow instance, namelyexternal service providers. Therefore, we introduce a service-oriented model. Webelieve that this model is better suited for cross-organizational workows while atthe same time being applicable in ordinary enterprise-wide workows. The basicentity in our model is a service. Informally, a service is an abstract specication ofthe amount of work that a resource promises to carry out with a specic qualityof service. A service species which part of a workow it covers. In general, aservice is not restricted to execute a single activity of a workow, it can spanmultiple activities. With A(S) we denote the set of activities covered by serviceS. With each service a service provider is associated. This can be either aninternal resource or an external organization. A service oered by an externalorganization is called an external service. Otherwise, it is called internal service.In contrast to internal services, external services are not executed under thecontrol of the service requester, i.e., the organization that runs and controls thecross-organizational workow. The service requester has only a limited possi-bility to get information on the state of an external service execution and toinuence this execution. Moreover, the internal work process of an external ser-vice might not be known to the service requester due to the autonomy of theservice providers. Thus, while they are executed, services have to be treated as\black boxes" from the viewpoint of a service requester. Only the interfaces toand from the services are known by the service requester and which activities aresubsumed by the service. This includes a specication how an external servicecan be invoked, which parameters have to be supplied, etc. Besides the inter-faces, a service description contains the quality of service oered by the serviceprovider to the service requester.ServiceWFMSInput dataOutput dataControl eventsService providerNotification eventsInquireService requesterFig. 1. Interfaces of a service and interaction with the WfMSFigure 1 illustrates our view on a service. A service S has four interfaces. Twoof them (Input and Output) are concerned with the data ow and two of them(Control and Notification) are concerned with control ow in form of controland notication events [6]. Control events (specied in the service description)can be sent by the service requester to the service provider in order to inuencethe processing of the service. Notication events are used to inform the servicerequester about the state of the processing of the external service. They can besent as a result of an internal event of the service provider or as a reaction to aninquiry of the service requester.3 Selection of Services in Cross-Organizational WorkowsIn this section, we discuss how services will be selected to execute the activitiesof the workow. We assume that all relevant information about services is madeavailable in a service repository. Therefore, we do not consider issues like ndingout which services are available.The workow and its activities have certain QoS parameters. Some of themare mandatory, others should be fullled as well as possible and are optimizedwith the following algorithms. For the sake of simplicity, we assume that thelatter parameters can be aggregated into a single value which can be used tocompare dierent service oers, i.e., each service S is assigned a value q whichwe call the price of the service. We further assume that this price can be calcu-lated for all services oered. In [7] we have described a technique how a servicerequester can derive and validate QoS parameters of an oered service based onthe observation of previous executions of this service.Since the control ow part of a workow specication establishes enablingconditions for activities, it is usually not clear at the start of a workow whichactivities actually have to be executed. For example, a workow can containbranches with alternative sequences of activities for certain parts of the work-ow. Conditions can be evaluated when all necessary parameters are availabledue to the execution of previous activities. Service selection mechanisms canbe dierentiated depending on when activities are assigned to services. In thispaper, we will consider the case where we assign only those activities to servicesof which, in the respective state of the workow, we know that they have to beexecuted. In [6] we have extended this mechanism to more complex subworkowswhich contain decisions yet to be made on which parts of the subworkow haveto be executed. We denote the part of workow W which can be outsourced attime t as Outsourcable(W; t).In the following, we describe an approach how to select services for the activ-ities in Outsourcable(W; t). Let  be the set of services which oer to cover anappropriate part of the workow in line with the specication of the workow.In particular, these services fulll all mandatory QoS parameters and executethe activities in an execution order that is in line with the workow specica-tion1. Additional restrictions can be included, e.g., the service requester mightwant to exclude the services of a certain service provider. The problem can thenbe formulated as nding a set of services from  which covers all activities inOutsourcable(W; t) exactly once, while optimizing the non-mandatory QoS pa-rameters. Mathematically, this problem is a minimal weighted exact set cover,i.e., can be formalized as follows: Find a subset O of , that forms an exact cover,i.e.,SS2OA(S) = Outsourcable(W; t) and 8Si; Sj2 O : A(Si) \ A(Sj) = ; andsuch that the cost of the coverPSi2Oqiis minimized. This problem is NP-complete [8{10]. However, since the set activities to be outsourced is usuallysmall, we expect that our approach is applicable to many real-world workows.In [6] we have described an algorithm how to select an optimal choice of services1Note, that this does not mean that the actual execution order has to be the same asin the workow specication. Due to the autonomy of the service provider and theresulting limited monotoring capabilities we only require that the execution ordercannot be distinguished at the interface of the service.A B C DSSSSS123 45Fig. 2. Services oered for a sub-workowService S1S2S3S4S5Price 5 4 2 3 2Fig. 3. Services and their pricesby solving the minimal weighted exact set cover. In the following we will give anexample of this approach.Figure 2 shows a simple subworkow consisting of four activities. We assumethat Outsourcable(W; t) = fA;B;C;Dg. There are ve services S1; : : : ; S5whichoer to perform parts of this subworkow. Figure 3 shows the prices of theseservices. A correct selection of services would be, for example, O1= fS3; S4; S5gas each activity is covered by exactly one service. The cost of this selectionis 7. Note that the cover fS1; S5g is not allowed as the activity C is includedin both services. However, besides O1there exists another exact cover namelyO2= fS2; S5g with cost 6. Thus, our algorithm returns O2as the optimum.Extensions of this technique for situations in which one activity is allowed to becovered by more than one service are discussed in [6].References1. D. Georgakopoulos, M. Hornick, and A. Sheth. An overview on workow manage-ment: From process modeling to workow automation infrastructure. Distributedand Parallel Databases, 3(2), April 1995.2. G. Alonso, D. Agrawal, A. El Abbadi, and C. Mohan. Functionality and limitationsof current workow management systems. IEEE Expert Journal, 12(5), 1996.3. S. Jablonski and C. Bussler. Workow Management | Modeling Concepts, Archi-tecture and Implementation. International Thomson Computer Press, 1996.4. A. Dogac, T.Oszu, A. Biliris, and T. Sellis, editors. Workow Management Systemsand Interoperability. NATO-ASI Series. Springer Verlag, 1998.5. A. Cichocki, S. Helal, M. Rusinkiewicz, and D. Woelk. Workow and ProcessAutomation - Concepts and Technology. Kluwer Academic Publishers, 1998.6. J. Klingemann, J. Wasch, and K. Aberer. Adaptive outsourcing in cross-organizational workows. GMD Report 30, GMD | German National ResearchCenter for Information Technology, 1998.7. J. Klingemann, J. Wasch, and K. Aberer. Deriving service models in cross-organizational workows. In Proceedings of RIDE-Information Technology for Vir-tual Enterprises, Sydney, Australia, March 1999.8. M. R. Garey and D. S. Johnson. Computers and Intractability | A Guide to theTheory of NP-Completeness. W. H. Freeman, New York, 1979.9. R. M. Karp. Reducibility among combinatorial problems. In R. E. Miller and J. W.Thatcher, editors, Complexity of Computer Computations, pages 85{103. PlenumPress, New York, 1972.10. D. S. Hochbaum, editor. Approximation Algorithms for NP-Hard Problems. PWSPublishing, Boston, 1997.

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