Orchestrating Web Services – Standards and Solutions

INTRODUCTION Standards and technological solutions for orchestration appeared as a natural growth of web service technologies. They arose out of the need for composing several services into one and thus forming more complex services and business processes. There is another term and group of technologies, relevant to composing of services – choreography. Choreography refers to global, multiparty, peer-to-peer collaborations where the component entities interact in long-lived stateful and coordinated way regardless of any programming model or supporting platform used. Choreography languages (examples are WSCI, WS-CDL, etc) are mainly descriptive and cannot be directly executed. These languages are necessary to be mapped to an orchestration language in order to be executed. Orchestration focuses on the behaviour of the composed services as a whole. Orchestration languages (e.g. BPLM, BPEL, XPDL, BPELJ, jPDL, etc) are executable languages and define a runtime environment for their execution. The paper is focused on orchestration and is organized as follows. The next section is devoted to the standards and technologies, related to orchestration of web services. After that the attention is paid on the software tools providing means for orchestration. The next is a case study about particular service orchestration software suits. The paper finishes with some concluding remarks.