<s>
In	O
artificial	B-Application
intelligence	I-Application
,	O
knowledge-based	O
agents	O
draw	O
on	O
a	O
pool	O
of	O
logical	O
sentences	O
to	O
infer	O
conclusions	O
about	O
the	O
world	O
.	O
</s>
<s>
At	O
the	O
knowledge	B-General_Concept
level	I-General_Concept
,	O
we	O
only	O
need	O
to	O
specify	O
what	O
the	O
agent	O
knows	O
and	O
what	O
its	O
goals	O
are	O
;	O
a	O
logical	O
abstraction	O
separate	O
from	O
details	O
of	O
implementation	O
.	O
</s>
<s>
This	O
notion	O
of	O
knowledge	B-General_Concept
level	I-General_Concept
was	O
first	O
introduced	O
by	O
Allen	O
Newell	O
in	O
the	O
1980s	O
,	O
to	O
have	O
a	O
way	O
to	O
rationalize	O
an	O
agent	O
's	O
behavior	O
.	O
</s>
<s>
It	O
chooses	O
actions	O
according	O
to	O
the	O
principle	B-General_Concept
of	I-General_Concept
rationality	I-General_Concept
.	O
</s>
<s>
Beneath	O
the	O
knowledge	B-General_Concept
level	I-General_Concept
resides	O
the	O
symbol	B-General_Concept
level	I-General_Concept
.	O
</s>
<s>
Whereas	O
the	O
knowledge	B-General_Concept
level	I-General_Concept
is	O
world	O
oriented	O
,	O
namely	O
that	O
it	O
concerns	O
the	O
environment	O
in	O
which	O
the	O
agent	O
operates	O
,	O
the	O
symbol	B-General_Concept
level	I-General_Concept
is	O
system	O
oriented	O
,	O
in	O
that	O
it	O
includes	O
the	O
mechanisms	O
the	O
agent	O
has	O
available	O
to	O
operate	O
.	O
</s>
<s>
The	O
knowledge	B-General_Concept
level	I-General_Concept
rationalizes	O
the	O
agent	O
's	O
behavior	O
,	O
while	O
the	O
symbol	B-General_Concept
level	I-General_Concept
mechanizes	O
the	O
agent	O
's	O
behavior	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
a	O
computer	O
program	O
,	O
the	O
knowledge	B-General_Concept
level	I-General_Concept
consists	O
of	O
the	O
information	O
contained	O
in	O
its	O
data	O
structures	O
that	O
it	O
uses	O
to	O
perform	O
certain	O
actions	O
.	O
</s>
<s>
The	O
symbol	B-General_Concept
level	I-General_Concept
consists	O
of	O
the	O
program	O
's	O
algorithms	O
,	O
the	O
data	O
structures	O
themselves	O
,	O
and	O
so	O
on	O
.	O
</s>
