<s>
A	O
knowledge-based	B-General_Concept
system	I-General_Concept
(	O
KBS	O
)	O
is	O
a	O
computer	B-Application
program	I-Application
that	O
reasons	O
and	O
uses	O
a	O
knowledge	O
base	O
to	O
solve	O
complex	O
problems	O
.	O
</s>
<s>
The	O
one	O
common	O
theme	O
that	O
unites	O
all	O
knowledge	B-General_Concept
based	I-General_Concept
systems	I-General_Concept
is	O
an	O
attempt	O
to	O
represent	O
knowledge	O
explicitly	O
and	O
a	O
reasoning	B-Application
system	I-Application
that	O
allows	O
it	O
to	O
derive	O
new	O
knowledge	O
.	O
</s>
<s>
Thus	O
,	O
a	O
knowledge-based	B-General_Concept
system	I-General_Concept
has	O
two	O
distinguishing	O
features	O
:	O
a	O
knowledge	O
base	O
and	O
an	O
inference	O
engine	O
.	O
</s>
<s>
The	O
first	O
part	O
,	O
the	O
knowledge	O
base	O
,	O
represents	O
facts	O
about	O
the	O
world	O
,	O
often	O
in	O
some	O
form	O
of	O
subsumption	O
ontology	O
(	O
rather	O
than	O
implicitly	O
embedded	O
in	O
procedural	O
code	O
,	O
in	O
the	O
way	O
a	O
conventional	O
computer	B-Application
program	I-Application
does	O
)	O
.	O
</s>
<s>
Other	O
approaches	O
include	O
the	O
use	O
of	O
automated	O
theorem	O
provers	O
,	O
logic	O
programming	O
,	O
blackboard	B-General_Concept
systems	I-General_Concept
,	O
and	O
term	O
rewriting	O
systems	O
such	O
as	O
CHR	O
(	O
Constraint	B-Application
Handling	I-Application
Rules	I-Application
)	O
.	O
</s>
<s>
Knowledge-based	B-General_Concept
systems	I-General_Concept
were	O
first	O
developed	O
by	O
artificial	B-Application
intelligence	I-Application
researchers	O
.	O
</s>
<s>
These	O
early	O
knowledge-based	B-General_Concept
systems	I-General_Concept
were	O
primarily	O
expert	B-Application
systems	I-Application
–	O
in	O
fact	O
,	O
the	O
term	O
is	O
often	O
used	O
interchangeably	O
with	O
expert	B-Application
systems	I-Application
,	O
although	O
there	O
is	O
a	O
difference	O
.	O
</s>
<s>
"	O
knowledge-based	B-General_Concept
system	I-General_Concept
"	O
refers	O
to	O
the	O
architecture	O
of	O
the	O
system	O
–	O
that	O
it	O
represents	O
knowledge	O
explicitly	O
,	O
rather	O
than	O
as	O
procedural	O
code	O
.	O
</s>
<s>
While	O
the	O
earliest	O
knowledge-based	B-General_Concept
systems	I-General_Concept
were	O
almost	O
all	O
expert	B-Application
systems	I-Application
,	O
the	O
same	O
tools	O
and	O
architectures	O
can	O
and	O
have	O
since	O
been	O
used	O
for	O
a	O
whole	O
host	O
of	O
other	O
types	O
of	O
systems	O
.	O
</s>
<s>
Virtually	O
all	O
expert	B-Application
systems	I-Application
are	O
knowledge-based	B-General_Concept
systems	I-General_Concept
,	O
but	O
many	O
knowledge-based	B-General_Concept
systems	I-General_Concept
are	O
not	O
expert	B-Application
systems	I-Application
.	O
</s>
<s>
The	O
first	O
knowledge-based	B-General_Concept
systems	I-General_Concept
were	O
rule	O
based	O
expert	B-Application
systems	I-Application
.	O
</s>
<s>
These	O
early	O
expert	B-Application
systems	I-Application
represented	O
facts	O
about	O
the	O
world	O
as	O
simple	O
assertions	O
in	O
a	O
flat	O
database	O
,	O
and	O
used	O
rules	O
to	O
reason	O
about	O
(	O
and	O
as	O
a	O
result	O
add	O
to	O
)	O
these	O
assertions	O
.	O
</s>
<s>
Later	O
architectures	O
for	O
knowledge-based	O
reasoning	O
,	O
such	O
as	O
the	O
BB1	O
blackboard	B-General_Concept
architecture	O
(	O
a	O
blackboard	B-General_Concept
system	I-General_Concept
)	O
,	O
allowed	O
the	O
reasoning	O
process	O
itself	O
to	O
be	O
affected	O
by	O
new	O
inferences	O
,	O
providing	O
meta-level	O
reasoning	O
.	O
</s>
<s>
Other	O
examples	O
of	O
knowledge-based	B-General_Concept
system	I-General_Concept
architectures	O
supporting	O
meta-level	O
reasoning	O
are	O
MRS	O
and	O
SOAR	B-Architecture
.	O
</s>
<s>
In	O
addition	O
to	O
expert	B-Application
systems	I-Application
,	O
other	O
applications	O
of	O
knowledge-based	B-General_Concept
systems	I-General_Concept
include	O
real-time	O
process	O
control	O
,	O
intelligent	O
tutoring	O
systems	O
,	O
and	O
problem-solvers	O
for	O
specific	O
domains	O
such	O
as	O
protein	O
structure	O
analysis	O
,	O
construction-site	O
layout	O
,	O
and	O
computer	O
system	O
fault	O
diagnosis	O
.	O
</s>
<s>
As	O
knowledge-based	B-General_Concept
systems	I-General_Concept
became	O
more	O
complex	O
,	O
the	O
techniques	O
used	O
to	O
represent	O
the	O
knowledge	O
base	O
became	O
more	O
sophisticated	O
and	O
included	O
logic	O
,	O
term-rewriting	O
systems	O
,	O
conceptual	O
graphs	O
,	O
and	O
frames	O
.	O
</s>
<s>
Frames	O
can	O
be	O
thought	O
of	O
as	O
representing	O
world	O
knowledge	O
using	O
analogous	O
techniques	O
to	O
object-oriented	B-Language
programming	I-Language
,	O
specifically	O
the	O
use	O
of	O
hierarchies	O
of	O
classes	O
and	O
subclasses	O
,	O
relations	O
between	O
classes	O
,	O
and	O
behavior	O
of	O
objects	O
.	O
</s>
<s>
For	O
example	O
,	O
procedures	O
stored	O
as	O
daemons	B-Operating_System
on	O
objects	O
could	O
fire	O
and	O
could	O
replicate	O
the	O
chaining	O
behavior	O
of	O
rules	O
.	O
</s>
<s>
Another	O
advancement	O
was	O
the	O
development	O
of	O
special	O
purpose	O
automated	B-Application
reasoning	I-Application
systems	I-Application
called	O
classifiers	B-Algorithm
.	O
</s>
<s>
The	O
most	O
recent	O
advancement	O
of	O
knowledge-based	B-General_Concept
systems	I-General_Concept
has	O
been	O
to	O
adopt	O
the	O
technologies	O
,	O
especially	O
a	O
kind	O
of	O
logic	O
called	O
description	B-Language
logic	I-Language
,	O
for	O
the	O
development	O
of	O
systems	O
that	O
use	O
the	O
internet	O
.	O
</s>
<s>
The	O
internet	O
often	O
has	O
to	O
deal	O
with	O
complex	O
,	O
unstructured	B-Application
data	I-Application
that	O
cannot	O
be	O
relied	O
on	O
to	O
fit	O
a	O
specific	O
data	O
model	O
.	O
</s>
<s>
The	O
technology	O
of	O
knowledge-based	B-General_Concept
systems	I-General_Concept
,	O
and	O
especially	O
the	O
ability	O
to	O
classify	O
objects	O
on	O
demand	O
,	O
is	O
ideal	O
for	O
such	O
systems	O
.	O
</s>
