11.1 General

NOTE: The content of this clause is REQUIRED for BPMN Choreography Modeling Conformance or for BPMN Complete Conformance. However, this clause is NOT REQUIRED for BPMN Process Modeling Conformance, BPMN Process Execution Conformance, or BPMN BPEL Process Execution Conformance. For more information about BPMN conformance types, see page 1.

A Choreography is a type of process, but differs in purpose and behavior from a standard BPMN Process. A standard Process, or an Orchestration Process (see page 143), is more familiar to most process modelers and defines the flow of Activities of a specific PartnerEntity or organization. In contrast, Choreography formalizes the way business Participants coordinate their interactions. The focus is not on orchestrations of the work performed within these Participants, but rather on the exchange of information (Messages) between these Participants.

Another way to look at Choreography is to view it as a type of business contract between two or more organizations.

This entails Message (document) exchanges in an orderly fashion: e.g., first a retailer sends a purchase order request to a supplier; next the supplier either confirms or rejects intention to investigate the order; then supplier proceeds to investigate stock for line-items and seeks outside suppliers if necessary; accordingly the supplier sends a confirmation or rejection back; during this period the retailer can send requests to vary the order, etc.

Message exchanges between partners go beyond simple request-response interactions into multi-cast, contingent requests, competing receives, streaming, and other service interaction patterns (REF for SIP). Moreover, they cluster around distinct scenarios such as: creation of sales orders; assignment of carriers of shipments involving different sales orders; managing the “red tape” of crossing customs and quarantine; processing payment and investigating exceptions. A Choreography is a definition of expected behavior, basically a procedural business contract, between interacting Participants (see page 111 for more information on Participants). It brings Message exchanges and their logical relation as Conversations into view. This allows partners to plan their Business Processes for inter-operation without introducing conflicts. An example of a conflict could arise if a retailer was allowed to send a variation on a purchase order immediately after sending the initial request. The Message exchange sequences in Choreography models need to be reflected in the orchestration Processes of participants. A Choreography model makes it possible to derive the Process interfaces of each partner’s Process (REF: Decker & Weske, 2007).

To leverage the familiarity of flow charting types of Process models, BPMN Choreographies also have “activities” that are ordered by Sequence Flows. These “activities” consist of one or more interactions between Participants. These interactions are often described as being message exchange patterns (MEPs). A MEP is the atomic unit (“Activity”) of a Choreography.

Some MEPs involve a single Message (e.g., a “Customer” requests an “Order” from a “Supplier”). Other MEPs will involve two Messages in a request and response format (e.g., a “Supplier” request a “Credit Rating” from a “Financial Institution,” who then returns the “Credit Rating” to the “Supplier”). There can be even more complex MEPs that involve error Messages, for example.

A single MEP can be defined as a BPMN Choreography Task (see page 323). Thus, a Choreography defines the order in which Choreography Tasks occur. Sub-Choreographies allow the composition/decomposition of

Choreographies.