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The second procedural concept that operational QVT offers are mappings
(see Figure 13). Mappings look quite similar to helpers, however, there is an
important difference. Mappings result in a link between the entity they are ap-
plied to and the entities they create. This means that a mapping can be called
several times but the structures it creates are only created once and that the
same structure can be mapped to different places (i.e. attributes of concepts)
in the model instance that is produced as a result of the QVT transformation.
In the mapping the variable msf holds all MessageFlows that are contained in
the actor and rmsf is the subset of MessageFlows in the set msf that are con-
sidered relevant. Relevant MessageFlows are those where a message is sent and
an answer is expected. The condition d.forkOperator
<>
null says that d sends
a message and the helper d.MsfSuccessor(msf) returns the set of message flows
that receive an answer for the message sent in d. This exactly corresponds to the
situation of the actor Sender in the communication pattern shown in Figure 10.
The MessageFlow sending the message would be considered relevant. The four
MessageFlows in the lower part would be returned by the helper MsfSuccessors.
If the communication pattern is only used once in the actors the sending Mes-
sageFlow in the actor Sender and the receiving MessageFlow in the Receiver
would be marked as initial message flows where the former is called the start
MessageFlow.
5 Use Cases
The presented approach for the design of multiagent systems is currently further
investigated and practically used in the research projects ISReal and COIN.
The COIN project investigates collaboration and interoperability for net-
worked enterprises. In this context we use the modelling approach presented in
this article for the design of negotiation processes in enterprise systems. Negoti-
ations occur prominently in business interactions between competing partners,
but also between cooperating partners, e.g. the participants in supply chains
or
virtual enterprises
. One scenario we are looking at in this work is the situa-
tion in which a production plan for collaborating partners in a supply chain has
already been scheduled. In this setting there are two scenarios for which addi-
tional negotiations could be necessary while a production plan is executed: (i)
for a specific step the service provider (e.g. a transportation service or a supplier
of raw material) has been left open or (ii) it turns out that a pre-negotiated
service provider cannot provide the agreed service. For both scenarios the Con-
tract Net Protocol (see Fig. 9) can be used to organize the negotiation. Services
the manager agent can chose from are registered and published in a
general ser-
vice platform (GSP)
which provides discovery and invocation support. Services
are semantically annotated using the WSMO/WSML language which facilitates
ad-hoc service provisioning and execution.
In COIN, service provision can be supported at design time and/or at run
time. In the first case, a process modeler can check for available services while
designing the interactions and agent plans. In the second case, when a service
