Service Interaction Patterns in business process:

choreographies are based on message exchange, and potentially many
participants interact in a choreography, while orchestrations are based on
control flow between the activities of a single process performed by a single
organization.
Service interaction patterns aim at filling this gap by proposing small granular
types of interactions that can be combined to process choreographies. As
with control flow patterns for process orchestrations, service interaction patterns
can also be used to benchmark languages for their ability to express
advanced conversations. Service interaction patterns can be classified according
to the following schemes.
� Number of participants involved: Bilateral interactions involve two participants,
whereas multilateral interactions involve more than two participants.
� Number of messages exchanged: Single transmission versus multi-transmission
interactions.
� Variations in message receiver : In case of two-way interactions, round-trip
interaction means that the receiver of the message is necessarily the same
as the sender, whereas routed interaction means that the receiver of the
message in general differs from the sender.
The Business Process Modeling Notation is used to provide graphical representations
of service interaction patterns. Since this notation is not specifically
tailored to the needs of service interaction patterns, the graphical representations
of the patterns are not complete. Together with the textual representation
of the patterns, the service interaction patterns are described properly.
Send
The send pattern represents a one-way interaction between two participants
seen from the perspective of the sender. There are different flavours of this
pattern, considering, for instance, the moment when the sender selects the
receiver: The receiver is known either at design time of the choreography or
only during the execution of a conversation.
Receive
The receive pattern also describes a one-way interaction between two participants,
but this time seen from the perspective of the receiver. In terms of
message buffering behaviour of the receiver, two cases can be distinguished.
Messages that are not expected are either discarded or stored until a later
point in time, when they can be consumed.
In the example shown in Figure 5.19 the facility management department
of a company receives a notification that the heating system in a building
does not work properly. The receipt of the message is represented by a start
message event. On occurrence of this event, a process orchestration is started
in the facility management that checks the heating system and tries to find
the source of the problem.
Send/Receive
In the send/receive pattern, a participant sends a request to another participant
who then returns a response message. Both messages belong to the same conversation. Since there could be several send/receive interaction instances
happening in parallel, corresponding requests and responses need to
be correlated.