A system already exists and a new party comes along and needs to plug into that system.
Examples are a new part supplier for an automobile manufacturer, and a new hotel chain for a global reservation system.
Lets take the travel related one. A global reservation system supports a number of processes for the query of hotel room/flight availability, reservations, cancellations etc.
What is needed when a new hotel chain, for example, wants to join this reservation system?
In order to plug into the reservation system, the various processes and interfaces have to be communicated; what business processes are supported by the system, what business process are expected to be provided by the hotel chain, what interfaces and protocols should be used, how transaction flow from one to the other etc.
This is clearly a “what is externally visible” scenario as the each side does not have to reveal the innards of their respective organizations.
What artifacts need to be defined? How are they defined?
The particular example is of a master/slave type of relationship where one partner (the global reservation system) dictates to another.
In some examples could be more peer-to-peer where the two parties sit down and define the shared processes together. Are any extra (or less) artifacts needed for this case?
A process invokes a number of web services in some order it defines to achieve a business objective.
Part of the process involves placing an order with a manufacturer and receiving a reply. However the process will not terminate until after the manufacturer has sent a shipping notice to the process. Since it may have to do several production runs to fulfill the order, the shipping notice may appear weeks or months later (or at some time agreed in some other business contract).
One way to architect this is through a callback scenario. The purchase order is sent to the manufacturer in one request, together with details of where the manufacturer can send the shipping notice when it is ready. The shipping notice can then be sent in its own request, but as part of the overall business process.
This scenario illustrates a very simple choreography requiring some description to somehow link two WSDL documents together.
It also requires the notion of a long running processes and state management.
An expansion of this scenario is if there is a sequence of exchanges between the two interfaces.