Business Process Execution Language
Wrote by IBM, Microsoft and BEA, the Business Process Execution Language for Web Services (BPEL4WS), commonly shortened to BPEL, is a language to define and execute definitions of business processes in XML.
Based on existing mapping rules of BPMN, the execution process definition in BPEL could be generated by graphical BPMN tools. In contrast to the graph oriented BPMN (like a flowchart), BPEL is highly block-structured like a programing language without an own graphical representation. So, only a subset of the BPMN 2.0 standard is supported with BPEL execution and the mapping problems between both standards is a matter of ongoing discussions.
Together with one or more WSDL files as part of the source code for a BPEL process, BPEL provides an easy and powerful web services integration.
BPEL and Human Workflow
BPEL 1.1 and also 2.0 doesn't integrate requirements for human driven workflow in the standard, because all interaction is based on web services. That means, that proprietary extensions must be implemented by the system developers, but this extensions are not covered by the standard.
To remedy this shortage, BPEL4People and WS Human Task were developed in 2005.