In a BPEL process service component, most pieces of data are in XML format. This includes the messages passed to and from the BPEL process service component, the messages exchanged with external services, and the local variables used by the process. You define the types for these messages and variables with the XML schema, usually in one of the following:

• Web Services Description Language (WSDL) file for the flow

• WSDL files for the services it invokes

• XSD file referenced by those WSDL files

Therefore, most variables in BPEL are XML data, and any BPEL process service component uses much of its code to manipulate these XML variables. This typically includes performing data transformation between representations required for different services, and local manipulation of data (for example, to combine the results from several service invocations).

BPEL also supports service data object (SDO) variables, which are not in an XML format, but rather in a memory structure format.