Process Choreography Implementation:

After discussing the design of process choreographies, this section looks at the
implementation of choreographies. Behavioural interfaces serve as blueprints
for the internal realization of process orchestrations, because each process orchestration
needs to expose an externally visible behaviour that was specified
as the behavioural interface of the respective participant.
Assume that there is a set of behavioural interfaces compatible with each
other. These interfaces can now be refined to local process orchestrations. In
local process orchestrations, activities can be added or, in some cases, even
reordered, while the observable behaviour has to be preserved.
The relationship between the behavioural interface and the local process
orchestration needs to be investigated, so that the correctness of the overall
collaboration can be achieved. Each local process orchestration needs to be
consistent with the respective behavioural interface definition. This section
will introduce consistency criteria using a business-to-business collaboration
scenario the supplier to the buyer.
As in the example discussed above, the auction is not public, so that
only registered parties can participate. Therefore, suppliers need to request
permission to participate in the auction beforehand. Once the auction has
started, suppliers can place their bids. When the auction completes, the buyer
selects a supplier according to the lowest bid or according to some other
evaluation criterion. Finally, the goods are shipped and payment is processed.
In this sample scenario, there are two alternatives for selecting a shipper:
either the selected supplier determines the shipper that would deliver the
goods to the buyer, or the supplier provides a list of shippers with different
transportation costs and quality levels, from which the buyer can choose a
shipper.
Each participant role can be potentially played by several process participants.
Each of these process participants develops a process orchestration.
These process orchestrations need to be consistent with the behavioural interface
of the participant role. For instance, the process orchestration of supplier
Su1 needs to be consistent with the behavioural interface (or with the behavioural
interfaces) of the Supplier role.
Using consistency rules, each participant can check locally whether its local
business process orchestration fits its behavioural interface. If the behavioural
interfaces are compatible with each other and if, in addition, for each
participant, the internal business process orchestration is consistent with its
behavioural interface, then a successful collaboration between the process participants
is realized�additional checks involving the internal business process
orchestrations of the participants are then not required.
The behavioural interface of a participant role leaves room for multiple
process orchestrations, i.e., there are multiple process orchestrations consistent
with a given behavioural interface.