XPDL vs BPEL

"BPEL and XPDL are entirely different yet complimentary standards. BPEL is an "execution language" designed to provide a definition of web services orchestration, specifically the underlying sequence of interactions, the flow of data from point-to-point. For this reason, it is best suited for straight-through processing or data-flows vis-a-vis application integration. The goal of XPDL is to store and exchange the process diagram, to allow one tool to model a process diagram, and another to read the diagram and edit, another to "run" the process model on an XPDL-compliant BPM engine, and so on. For this reason, XPDL is not an executable programming language like BPEL, but specifically a process design format that literally represents the "drawing" of the process definition. To wit, it has ‘XY' or vector coordinates, including lines and points that define process flows. This allows an XPDL to store a one-to-one representation of a BPMN process diagram. For this reason, XPDL is effectively the file format or "serialization" of BPMN, as well as any non-BPMN design method or process model which use in their underlying definition the XPDL meta-model (there are presently about 50 tools which use XPDL for storing process models.)"


"XPDL is an interchange format, you can use it to exchange the business process diagrams among different tools. BPEL is an execution language of the business process and you don't use it to exchange diagrams because it cannot store graphical information about the diagram"


"BPEL is originally more an orchestration language for WebServices than a Business Process definition language. Compared to XPDL, BPEL is much more technical, much more difficult to read, much more difficult to write. BPEL is almost a scripting language that inherits from webservices problematics, XPDL is a true descriptive language dedicated to Business Processes."

"The purpose of XPDL is to capture the layout of the process and the essential information necessary to make it "run".

BPEL and XPDL are complementary. You may use XPDL to move your BPMN diagram from a drawing tool to a workflow platform, and the workflow platform might use BPEL internally to store the process for execution. BPEL is XML scripting for web services orchestration, and some tools extend this to allow for user interactions (+ BPEL4People/WS-HumanTask are intended to help there). If you want to move the diagram to another platform, you can use XPDL. BPEL doesn't store layout information by default, so a BPEL process will most likely be rendered very differently if moved from one platform to the other. XPDL is designed to preserve the layout."

Source:
http://www.ebizq.net/blogs/column2/2007/03/xpdl_and_bpel.php
http://www.bpm-research.com/forum/index.php?showtopic=827