Information Technology Reference
In-Depth Information
(1)
A
is the action name;
(2)
x
1
, …, x
n
are individual variables, which denote the objects on which the
action operates;
(3)
P
A
is the set of
pre-conditions
, which must be satisfied before the action is
executed, i.e.
P
A
= {con | con∈ condition};
(4)
E
A
is the set of post-conditions, which denotes the effects of the action;
E
A
is
a set of pair
head/body
, where head= {con | con∈condition}, body is a
condition.
Remark:
(1) Action defines the transition relation of state, i.e. an action A transits a state u
to a state v, if action A can produce state v under state u. The transition
relation depends on whether states u, v satisfy the pre-conditions and
post-conditions of action A. The transition relation is denoted as u TA v.
(2) Because some states that happened before action A may influence
post-condition of action A, there is some difference between pre-conditions
and post-conditions. As to post-conditions head/body, if each condition of
head can be satisfied in state u, then each condition of body can also be
satisfied in state v.
Definition 2.34
Let
A
(
1
x
,...,
x
)
≡
(
P
,
E
)
be a action description and let
n
A
A
A(a
1
, …, a
n
)
be the substitution of A(x
1
, …, x
n
)
by
{a
1
/x
1
, …, a
n
/x
n
}
.
Then
A(a
1
, …,
a
n
)
is called an action instance of
A(x
1
, …, x
n
). A(a
1
, …, a
n
)is called atom action
,
P
A
(a
1
, …, a
n
) is the precondition of A(a
1
, …, a
n
)
and
E
A
(a
1
, …, a
n
)
is the result set
of
A(a
1
, …, a
n
).
Definition 2.35
Actions in DDL are defined as follows:
(1) Atomic action A(a
1
, …, a
n
) is action;
