Introduction
JBoss jBPM is a flexible, extensible framework for process languages. jPDL is one process language that is build on top of that common framework.
Overview of the jPDL components
The jPDL graphical process designer
jPDL also includes a graphical designer tool. The designer is a graphical tool for authoring business processes. It's an eclipse plugin.
The jBPM core library
The JBoss jBPM core component is the plain java (J2SE) library for managing process definitions and the runtime environment for execution of process instances.
Depending on the functionalities that you use, the library lib/jbpm-jpdl.jar has some dependencies on other third party libraries such as e.g. hibernate, dom4j and others.
For its persistence, jBPM uses hibernate internally.
The JBoss jBPM API can be accessed from any custom java software in your project, like e.g. your web application, your EJB's, your web service components, your message driven beans or any other java component.
The JBoss jBPM Job Executor
The job executor is a component for monitoring and executing jobs in a standard Java environment.
The job executor component is packaged in the core jbpm-jpdl library, but it needs to be deployed in one of the following ways: either register the JobExecutorLauncher servlet context listener in the web app deployment descriptor to start/stop the job executor during creation/destruction of the servlet context, or start up a separate JVM and start the job executor in there programatically.