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4 RELATED WORK
The most relevant work is the FIPA modelling
standard in deployment and mobility of multi-agent
systems (FIPA Modeling TC, 2003), which uses
activity diagrams and deployment diagrams as part
of AUML. AUML deployment diagrams statically
models movement of agents by incorporating a new
association with a stereotype <<moves>> and nods
in a network in which agents are modelled as
software components. Algorithmic behaviour of an
agent is modelled in an ordinary Activity diagram,
but movement is captured by using symbols for a
node and a decision which an agent will take in
order to migrate different nodes in a network.
Lind adopted UML Activity diagrams to model
agent interaction protocol without introducing any
new modelling elements (Lind, 2002). He used
swimlane as a construct which denotes a role of an
agent and synchronous communications by giving
new stereotypes. However, as mobile agent systems
being inherently multi-agent, it is hard to use his
notation for more complex communication patterns,
which require more channels between different
agents.
The most recent approach (Baumeister, et. al.,
2002) related to ours is an extension of UML class
diagram and activity diagrams to model mobile
system. Their notation, which is based on a mobile
calculus mobile ambient (Cardelli and Gordon,
1998), assumes both mobile objects and locations
could migrate to another location. The crucial
difference between ours and theirs is that we use a
different mobility model in which we do not allow a
location to move to another location while some
agents running in parallel.
The biggest advantage of our work is its
straightforward visual representation of mobility of
agent, which helps to capture dynamic and
algorithmic behaviour of mobile agents and to
understand how they interact with each other in
terms of locality.
5 CONCLUSION AND FURTHER
WORK
In this paper, we presented extensions to activity
diagram for modelling mobile agent applications. A
new stereotype <<Host>> + parameter for swimlane,
which represents the location is introduced in order
to capture mobility of agents. Other specific features
of agents such as communications, cloning are
defined by existing model elements with a new rule
of subactivities. We also proposed a new notation
subswimlane in order to model nested places.
One of drawbacks is that an activity diagram
basically models a single multi-threaded agent. Even
our proposed notation clearly visualize locality and
communications between agents, it is hard to verify
all communications and movement are eventually
synchronized between agents. The best way to
overcome this drawback is to translate activity
diagrams into some other formalism such as process
algebra, which provide verification procedure of the
model. Fortunately our concept of location can be
easily mapped into mobile calculi, such as mobile
ambient, which provides verification procedure as
well as semantic foundations of our notation.
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