BPEL4WS supports extensibility by allowing namespace-qualified attributes to appear on any BPEL4WS element and by allowing elements from other namespaces to appear within BPEL4WS defined elements. This is allowed in the XML Schema specifications for BPEL4WS.
Extension elements can be used to exchange application-specific data on top of message flows already defined in this specification. This addresses the need to exchange such data as isolation-level supported signatures or other information related to business-level coordination protocols. The data can be logged for auditing purposes, or evaluated to ensure that a decision meets certain business-specific constraints.