In this chapter we provided a survey of the most important topics regarding flexible workflow management in service-oriented environments. Flexibility in workflow management becomes more and more important due to shorter product life-cycles.
Companies are required to adapt their business processes in shorter time cycles. This implies that the supporting IT-infrastructure must quickly adapt itself to changing business processes. The concept of loose coupling in service-oriented architectures provides a means to cope with the required flexibility to adapt to changing business requirements.
Flexible business process support is required for both internal processes deliv-ering customer value and inter-organizational processes co-ordinating the interac-tions with business partners. These two views on business processes are addressed in service-oriented environments by the concepts of orchestration and choreogra-phy. Accordingly, we demonstrated how orchestration and choreography are sup-ported in service-oriented architectures. Furthermore, we explicitly show the inter-dependencies between orchestrated and choreographed processes.
Orchestration and Choreography are abstract concepts to describe business pro-cesses. These concepts are independent of the underlying IT-systems. We briefly discussed relevant standard languages in the web services world used to describe orchestrations and choreographies in a machine-readable way to be processed by workflow systems. Currently, the business process execution language (BPEL) is the most commonly supported language by tools and workflow systems. Accord-ingly, we used BPEL to show how orchestrations and choreographies are presented in a language that is compatible to the web services approach.
Today, orchestrations and choreographies are specified at design time and in-stances at run time have to follow the specifications made at design time. In order to increase the flexibility in web services-based workflows agents may assist in the construction of workflows at design time and to cope with dynamic adjustments at run time. We discussed agent-based approaches to search and select services being part of an orchestration as well as to construct the execution order within the orchestration. Furthermore, we highlighted agent-based approaches to establish choreographies between business partners that have not conducted electronic busi-ness processes before.
We elaborated on the need to dynamically support the execution of web services workflows. Since the current approach taken by BPEL describes a static binding to operations, port types, and partner links, dynamically bindings to the best service provider are not supported. We introduced two major approaches found in the lit-erature overcoming this problem. One is based on redirecting the call of services requiring these dynamics to a special service that performs the dynamic binding.
The other one is based on extensions to BPEL allowing dynamic bindings.
Frequently adapting business processes to changing requirements results in mul-tiple schema versions of a workflow. Accordingly, we discussed approaches to schema evolution. This covers solutions to dynamically adapting running instances of an orchestration to an updated schema version. In addition, we focused on the ef-fect of schema evolution in orchestrations of private processes on the choreography of dependent inter-organizational processes.
This survey highlights the different aspects to be considered in flexible workflow management. However, solutions for the different aspects have been developed in isolation from each other. Consequently, these solutions are not well aligned to each other. This requires a fine tuning of the referenced approaches to become comple-mentary to each other. Thus, this survey may serve as a starting point to deliver a well-aligned framework to implement a flexible workflow management by means of web services.
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Semantics for Service-Oriented Architectures
Michael Stollberg and Dieter Fensel
Abstract The concept of Service-Oriented Architectures (SOA) is the latest de-sign paradigm for IT systems. The aim is to use Web services as the basic building blocks, which provide reusable functionalities that are invokable over the Internet.
The initial Web service technology stack around WSDL, SOAP, and UDDI enables the technical provision and usage of Web services. However, the support for the detection of the suitable Web services for a specific client application is limited to manual inspection. To better support this for SOA applications with the larger numbers of available Web services that can be expected in real-world scenarios, the emerging concept of Semantic Web services (SWS) develops inference-based tech-niques for the automated discovery, composition, and execution of Web services.
This chapter provides an overview on the SWS approach as well as the latest tech-nology developments.
5.1 Introduction
The concept of Web services as been invented by a consortium of leading IT vendors in the late 1990s. Essentially, a Web service is a program that can be invoked over the Internet. It is accessible via an interface that specifies the physical address as well as the messages via which a client can consume the Web service. The actual con-sumption is realized by the exchange of XML data over the Web via SOAP. Remain-ing independent of the actual implementation, this technology facilitates computRemain-ing
Michael Stollberg
SAP Research CEC Dresden, SAP AG, Dresden D-01187, Germany e-mail:michael.stollberg@sap.com
Dieter Fensel
Semantic Technology Institute (STI), University of Innsbruck, Innsbruck Austria e-mail:dieter.fensel@sti2.at
N. Griffiths, K.-M. Chao (eds.),Agent-Based Service-Oriented Computing, 113 Advanced Information and Knowledge Processing,
DOI 10.1007/978-1-84996-041-0 5, cSpringer-Verlag London Limited 2010
over the Web as well as seamless information exchange and reuse functionalities within and between organizations.
Because of this, Web services have been proclaimed as the core technology for Service-Oriented Architectures (SOA). In the future, IT systems shall be composed of Web services as the basic building blocks instead of proprietary solutions. The aim is to exploit the potential of the World Wide Web (WWW) as an infrastruc-ture for computation, and also to reduce the development and maintenance costs for IT systems. The adaptation of Web services and the SOA paradigm within indus-try as well as by non-profit software developers has been facilitated by the early standardization of the necessary technologies. Commonly referred to as the initial Web service technology stack, these are (1) theWeb Service Description Language (WSDL) for specifying the technical information, as well as the messages for in-voking and consuming a Web service, (2) SOAP as a messaging technology for exchanging XML data over the Web, and (3) the Universal Description, Discov-ery and Integration Protocol(UDDI) which provides a registry technology for Web services.
This allows service providers to offer functionalities as Web services, and also supports the technical usage of Web services by clients. However, the descriptions remain on a syntactic level which limits the Web service usage to manual inspection:
the developer of a client application needs to search for a suitable Web service within a UDDI repository, then inspect the WSDL description in order to determine how and in which order the necessary messages shall be exchanged, and finally integrate the Web service invocation into the application.
In order to overcome these deficiencies, the emerging concept of Semantic Web services (SWS) develops techniques for better supporting the detection and usage of Web services on the basis of semantic descriptions. The aim is to better sup-port and eventually automate the Web service usage process, and to facilitate the dynamic detection and execution of the necessary Web services for solving a par-ticular client request within SOA systems. For this, inference-based techniques for automateddiscoveryas the detection of suitable candidates out of the available Web services,compositionas the automated combination of several Web services, and the automated executionof Web services are developed. The SWS approach uses ontologies as the underlying data model, which are formally specified knowledge models propagated as the base technology for the Semantic Web—another promi-nent amendment of the existing Web.
This chapter provides an overview of the SWS approach as well as the latest technology developments for this. Firstly, Section 5.2 recalls the initial Web service technologies and the vision of Service-Oriented Architectures. Then, Section 5.3 introduces the concept and the most prominent frameworks for Semantic Web ser-vices, and Section 5.4 presents recent developments on SWS techniques for au-tomating the detection, usability analysis, and execution of Web services. Finally, Section 5.5 summarizes the chapter and outlines perspectives for the future devel-opment and standardization of semantic SOA technologies.