Information Technology Reference
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4Exampe
Let us consider the following simple example. We shall specify an online social
network, in which users may register themselves and interact.
3
The objective
of the specification is to test advertisement strategies through simulation. To
this end, we define an environment
AG, AT, EB
with
n
agents, such that each
agent
ag
i
∈
AG
is capable of performing the action
buy
(i.e., to buy the ad-
vertised product) and
sendM sg
(i.e., to send some message to another agent),
as well as receiving the stimuli
gui
1
,
gui
2
(i.e., the graphical user interface of
the website can be set in two different ways),
ad
1
,
ad
2
(i.e., there are two dif-
ferent possible advertisements) and
msg
(i.e., a message received). Formally,
ag
i
=
.
The action transformers among the agents allow them to send messages
to their friends. Of course, the particular topology of this network can vary,
but in essence each agent
ag
i
shall have some action transformers of the form
i,
{
gui
1
,gui
2
,ad
1
,ad
2
,msg
}
,
{
buy, sendMsg
}
. The effect of such a message could be similar to that
of an advertisement (i.e., a product recommendation by a friend).
Finally, and most importantly, for each agent
ag
ag
i
,sendMsg,msg,ag
j
∈
AG
, we define the following
new environment behavior
eb
i
∈
EB
:
(
BeginStimulation
(
gui
1
,ag
i
)+
BeginStimulation
(
gui
2
,ag
i
));
ad
2
,ag
i
))
These
eb
i
specify four possible simulation sequences concerning each agent. For
instance, in some simulation run, agent
ag
1
could be stimulated by
BeginStimulation
(
Stimulate
(
ad
1
,ag
i
)+
Stimulate
(
. However, it could
be that this particular sequence would be ineffective in eliciting the agent's
buy
action, in which case another sequence could be tried. The important thing,
though, is that these trials can all be performed automatically, since they are
explicit in the environment definition. This shows how EMMAS can endow sim-
ulators with some formal verification capabilities.
(
gui
1
,ag
1
)
and then by
Stimulate
(
ad
1
,ag
1
)
5Con lu on
In this paper we have presented a formalization for environments of MASs. We
provided a high-level description for this formalization, with a semantics given
using the
π
-calculus. We found necessary to perform some adjustments on the
standard behavior induced by the
π
-calculus' operational semantics in order to
allow its integration with the remaining parts of the proposed approach. Further-
more, we avoided explicit temporal references in this formalization. However, it
should be possible to add an explicit notion of time to EMMAS, though this
would introduce new complications as well.
The presented environments have both structural and operational aspects.
That is to say, they represent certain structures, which can then be changed by
3
Actual
examples
of
such
networks
include
popular
websites
such
as
www.facebbok.com
,
www.orkut.com
and
www.myspace.com
.
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