The WS-BPEL 2.0 standard provides the possibility to add activities for specific usage. These extensions can be formalized in a BPEL process with the following mechanism:

We define an extension as following:

The namespace attribute corresponds to the namespace of the extended activity. The mustUnderstand attribute specifies if the BPEL engine must understand the extended
activity (that is mandatory for the process to be successfully executed) or if it can ignores it (i.e. a debug activity).

Then the extended activity can be placed in the BPEL process, embedded in a <bpel:extensionActivity></bpel:extensionActivity> couple of tags.