Essential Business Process Modeling

WSCL

WSCL, the least well-known of the choreography approaches, is easy to miss in the hunt for BPM standards. Its 24-page specification, submitted by Hewlett Packard to the W3C in the spring of 2002^[*] (ancient history, in BPM timelines), has never caught on with vendors and has not permeated the W3C’s current choreography efforts. It’s too bad, because WSCL’s simple, elegant approach to choreography, using the idea of the state machine, has considerable merit.

WSCL is an XML language whose main construct is a conversation, which represents a participant’s web-service-based dialog with the other participants in the attainment of a business goal. The steps of the conversation are called interactions, in which the participant either calls or is called by other participants. WSCL supports four types of interactions, which are summarized in Table 8-2.

Table 8-2. WSCL interactions

WSCL type	WSDL type	Content	Description
Receive	One-way	Input message	Participant reacts to an inbound request message.
Send	Notification	Output message	Participant sends a message outbound.
Receive-send	Request-response	Input message, output message, multiple output fault messages	Participant reacts to an inbound request message and sends back a response message.
Send-receive	Solicit-response	Output message, input message, multiple input fault messages	Participant sends a message outbound and waits for the response to come back.

The link from one interaction (the source) to another (the destination) is called a transition. In the ...