This part of the book talks about how to take one or more services and compose them to form a new service. The figure that follows shows where this topic falls in the stack of Web services specifications.

This area brings you to a new level of complexity, starting with how different services can be aggregated into more sophisticated higher-level services. Chapter 14, “Modeling Business Processes: BPEL” presents the Web Services Business Process Execution Language specification (WS-BPEL, better known as BPEL), which is being standardized at OASIS. BPEL enables service aggregations to be defined in both an abstract and an executable manner. A handful of other specifications that address different aspects or styles of composition have been proposed; however, BPEL is at this point the only one with significant following in the industry.