Web service orchestration with BPEL

Softwareengineersareincreasinglyadoptingserviceorientedar-chitectures (SOAs) for the automation of business processes andthe integration of IT systems, both within and across organisa-tional boundaries. These service oriented architectures frequentlyrely on web service standards, such as the Web Service Descrip-tion Language (WSDL) [5] and the Simple Object Access Protocol(SOAP) [10] for the implementation of service invocations acrossmachine boundaries.The combination of several web services into a more complexweb service is a crucial building block for service oriented archi-tectures. Peltz refers to such compositions that integrate the in-vocation of two or more services into a more complex executableworkflow as web service orchestration and contrasts this with webservice choreography, which tracks message exchanges betweendifferent autonomous domains [13]. Web service orchestration isappealing as it facilitates compositionality and reuse of the compo-nents that implement these services without necessarily having todeploy these services locally.Web service orchestration is supported by the Business ProcessExecution Language for Web Services (BPEL) [1]. BPEL emergedthrough consolidation of earlier work on IBM’s Web Service FlowLanguage (WSFL) [11] and XLANG [14] developed by Microsoft.BPELwas proposedas astandardby Microsoft, IBM,Siebel, BEA