Information Technology Reference
In-Depth Information
t
. Although this may often not be necessary, this definition keeps the
possibility open.
As agent-based models are often used for representing complex
systems, interactions between entities are a very important aspect. As
entities (agents as well as objects) are situated within the environment,
actions of agents as well as interactions are often also influenced by
the environment. Therefore, it is often required, to define a metric on
the environment which is a function
m
defining the distance between
two points:
m
:
L
×
L
→
R
. As a metric is not always necessary, the
GRAMS reference model does not require its definition.
The set
denotes
environmental properties
(e.g., tem-
perature, humidity, gravitation) which are associated with specific
locations:
P
=
{
p
i
}
p
i
:
L
→D
i
(6.1)
D
i
denotes the actual domain of the property
p
i
. For example, tem-
perature might be modeled by discrete values in degrees Celsius, while
humidity may be represented by continuous values in percent. The
actual value of all properties at time
t
is denoted by
S
t
(
P
).
To model environmental dynamics properties of each location may
be altered by
environmental update functions
u
i
∈
U
:
u
i
:
L
×
P
→
P
(6.2)
As defined later on, update functions are triggered by events and may
trigger new events themselves. Each update function has a duration
which represents the time interval from triggering until the actual
state change. An update function may also trigger itself again.
S
t
(
U
)
denotes the state of all update functions at a point in time
t
.
As the environment may change over time, the state of the environ-
ment is always only defined for a specific point in time:
Definition 13 (State of the environment)
The state
S
of the en-
vironment
E
at a point in time
t
is
S
t
(
E
)=(
S
t
(
L
)
,S
t
(
P
)
,S
t
(
U
)).
