<s>
A	O
deductive	B-Algorithm
classifier	I-Algorithm
is	O
a	O
type	O
of	O
artificial	B-Application
intelligence	I-Application
inference	O
engine	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
names	O
of	O
classes	B-Application
,	I-Application
sub-classes	I-Application
,	O
properties	O
,	O
and	O
restrictions	O
on	O
allowable	O
values	O
.	O
</s>
<s>
Classifiers	O
are	O
also	O
similar	O
to	O
theorem	B-Application
provers	I-Application
in	O
that	O
they	O
take	O
as	O
input	O
and	O
produce	O
output	O
via	O
First	O
Order	O
Logic	O
.	O
</s>
<s>
Classifiers	O
originated	O
with	O
KL-ONE	B-Language
Frame	O
languages	O
.	O
</s>
<s>
Modern	O
classifiers	O
leverage	O
the	O
Web	B-Language
Ontology	I-Language
Language	I-Language
.	O
</s>
<s>
A	O
classic	O
problem	O
in	O
knowledge	O
representation	O
for	O
artificial	B-Application
intelligence	I-Application
is	O
the	O
trade	O
off	O
between	O
the	O
expressive	O
power	O
and	O
the	O
computational	O
efficiency	O
of	O
the	O
knowledge	O
representation	O
system	O
.	O
</s>
<s>
As	O
a	O
result	O
of	O
this	O
trade-off	O
,	O
a	O
great	O
deal	O
of	O
early	O
work	O
on	O
knowledge	O
representation	O
for	O
artificial	B-Application
intelligence	I-Application
involved	O
experimenting	O
with	O
various	O
compromises	O
that	O
provide	O
a	O
subset	O
of	O
FOL	O
with	O
acceptable	O
computation	O
speeds	O
.	O
</s>
<s>
Rule-based	O
systems	O
were	O
the	O
predominant	O
knowledge	O
representation	O
mechanism	O
for	O
virtually	O
all	O
early	O
expert	B-Application
systems	I-Application
.	O
</s>
<s>
A	O
classifier	O
could	O
analyze	O
a	O
class	B-Application
hierarchy	I-Application
(	O
also	O
known	O
as	O
an	O
ontology	O
)	O
and	O
determine	O
if	O
it	O
was	O
valid	O
.	O
</s>
<s>
The	O
first	O
language	O
to	O
successfully	O
demonstrate	O
a	O
classifier	O
was	O
the	O
KL-ONE	B-Language
family	O
of	O
languages	O
.	O
</s>
<s>
The	O
LOOM	B-Language
language	I-Language
from	O
ISI	O
was	O
heavily	O
influenced	O
by	O
KL-ONE	B-Language
.	O
</s>
<s>
LOOM	B-Language
also	O
was	O
influenced	O
by	O
the	O
rising	O
popularity	O
of	O
object-oriented	O
tools	O
and	O
environments	O
.	O
</s>
<s>
Loom	B-Language
provided	O
a	O
true	O
object-oriented	O
capability	O
(	O
e.g.	O
</s>
<s>
The	O
Web	B-Language
Ontology	I-Language
Language	I-Language
provides	O
a	O
formalism	O
that	O
can	O
be	O
validated	O
and	O
reasoned	O
on	O
via	O
classifiers	O
such	O
as	O
Hermit	O
and	O
Fact++	B-Language
.	O
</s>
<s>
The	O
earliest	O
versions	O
of	O
classifiers	O
were	O
logic	B-Application
theorem	I-Application
provers	I-Application
.	O
</s>
<s>
The	O
first	O
classifier	O
to	O
work	O
with	O
a	O
Frame	O
language	O
was	O
the	O
KL-ONE	B-Language
classifier	O
.	O
</s>
<s>
A	O
later	O
system	O
built	O
on	O
common	O
lisp	O
was	O
LOOM	B-Language
from	O
the	O
Information	O
Sciences	O
Institute	O
.	O
</s>
<s>
LOOM	B-Language
provided	O
true	O
object-oriented	O
capabilities	O
leveraging	O
the	O
Common	O
Lisp	O
Object	O
System	O
,	O
along	O
with	O
a	O
frame	O
language	O
.	O
</s>
<s>
In	O
the	O
Semantic	O
Web	O
the	O
Protege	B-Language
tool	O
from	O
Stanford	O
provides	O
classifiers	O
(	O
also	O
known	O
as	O
reasoners	O
)	O
as	O
part	O
of	O
the	O
default	O
environment	O
.	O
</s>
