Tutorial 3: Manipulating XML Documents in BPEL In a BPEL process, everything is XML, including the messages that are passed into and returned from the BPEL process, the messages that are exchanged with external services, and any local variables used by the flow itself. The types for all of these messages and variables are defined with XML Schema, usually in the WSDL file for the flow itself or in the WSDL files for services it invokes. Therefore, all variables in BPEL are XML documents, and any interesting BPEL process will spend a fair amount of its code manipulating those XML variables. Typically this includes doing data transformation between representations required for different services, as well as local manipulation of data (for example, to concatenate the results from several service invocations together). This document provides further details, primarily regarding the large part XPath plays in manipulating XML data.