<s>
F-logic	B-Language
(	O
frame	O
logic	B-Language
)	O
is	O
a	O
knowledge	O
representation	O
and	O
ontology	B-Language
language	I-Language
.	O
</s>
<s>
F-logic	B-Language
combines	O
the	O
advantages	O
of	O
conceptual	O
modeling	O
with	O
object-oriented	B-Language
,	O
frame-based	O
languages	O
and	O
offers	O
a	O
declarative	O
,	O
compact	O
and	O
simple	O
syntax	O
,	O
as	O
well	O
as	O
the	O
well-defined	O
semantics	O
of	O
a	O
logic-based	O
language	O
.	O
</s>
<s>
Features	O
include	O
,	O
among	O
others	O
,	O
object	O
identity	O
,	O
complex	O
objects	O
,	O
inheritance	B-Language
,	O
polymorphism	B-Application
,	O
query	O
methods	O
,	O
encapsulation	B-Application
.	O
</s>
<s>
F-logic	B-Language
stands	O
in	O
the	O
same	O
relationship	O
to	O
object-oriented	B-Language
programming	I-Language
as	O
classical	O
relational	B-Application
calculus	I-Application
stands	O
to	O
relational	B-Application
database	I-Application
programming	O
.	O
</s>
<s>
F-logic	B-Language
was	O
developed	O
by	O
Michael	O
Kifer	O
at	O
Stony	O
Brook	O
University	O
and	O
Georg	O
Lausen	O
at	O
the	O
University	O
of	O
Mannheim	O
.	O
</s>
<s>
F-logic	B-Language
was	O
originally	O
developed	O
for	O
deductive	O
databases	O
,	O
but	O
is	O
now	O
most	O
frequently	O
used	O
for	O
semantic	O
technologies	O
,	O
especially	O
the	O
semantic	O
web	O
.	O
</s>
<s>
F-logic	B-Language
is	O
considered	O
as	O
one	O
of	O
the	O
formalisms	O
for	O
ontologies	B-Language
,	O
but	O
description	B-Language
logic	I-Language
(	O
DL	O
)	O
is	O
more	O
popular	O
and	O
accepted	O
,	O
as	O
is	O
the	O
DL-based	O
OWL	B-Language
.	O
</s>
<s>
A	O
development	O
environment	O
for	O
F-logic	B-Language
was	O
developed	O
in	O
the	O
NeOn	O
project	O
and	O
is	O
also	O
used	O
in	O
a	O
range	O
of	O
applications	O
for	O
information	O
integration	O
,	O
question	B-Algorithm
answering	I-Algorithm
and	O
semantic	O
search	O
.	O
</s>
<s>
Prior	O
to	O
the	O
version	O
4	O
of	O
Protégé	O
ontology	B-Language
editor	O
,	O
F-Logic	B-Language
is	O
supported	O
as	O
one	O
of	O
the	O
two	O
kinds	O
of	O
ontology	B-Language
.	O
</s>
<s>
The	O
frame	O
syntax	O
of	O
the	O
Rule	B-Language
Interchange	I-Language
Format	I-Language
Basic	O
Logic	B-Language
Dialect	O
(	O
RIF	O
BLD	O
)	O
standardized	O
by	O
the	O
World	O
Wide	O
Web	O
Consortium	O
is	O
based	O
on	O
F-logic	B-Language
;	O
RIF	O
BLD	O
however	O
does	O
not	O
include	O
non-monotonic	O
reasoning	O
features	O
of	O
F-logic	B-Language
.	O
</s>
<s>
In	O
contrast	O
to	O
description	B-Language
logic	I-Language
based	O
ontology	B-Language
formalism	O
the	O
semantics	O
of	O
F-logic	B-Language
are	O
normally	O
that	O
of	O
a	O
closed	B-Application
world	I-Application
assumption	I-Application
as	O
opposed	O
to	O
DL	O
's	O
open	B-Application
world	I-Application
assumption	I-Application
.	O
</s>
<s>
the	O
SHOIN	B-Language
description	I-Language
logic	I-Language
that	O
OWL	B-Language
DL	I-Language
is	O
based	O
on	O
is	O
decidable	O
.	O
</s>
<s>
However	O
it	O
is	O
possible	O
to	O
represent	O
more	O
expressive	O
statements	O
in	O
F-logic	B-Language
than	O
are	O
possible	O
with	O
description	B-Language
logics	I-Language
.	O
</s>
<s>
The	O
most	O
comprehensive	O
description	O
of	O
F-logic	B-Language
was	O
published	O
in	O
1995	O
.	O
</s>
<s>
Classes	O
and	O
individuals	O
may	O
be	O
defined	O
in	O
F-logic	B-Language
as	O
follows	O
:	O
</s>
<s>
In	O
addition	O
it	O
is	O
possible	O
to	O
represent	O
axioms	O
in	O
F-logic	B-Language
in	O
the	O
following	O
manner	O
:	O
</s>
<s>
The	O
Flora-2	B-Language
system	O
introduced	O
a	O
number	O
of	O
changes	O
to	O
the	O
syntax	O
of	O
F-logic	B-Language
,	O
making	O
it	O
more	O
suitable	O
for	O
a	O
knowledge	O
representation	O
and	O
reasoning	O
system	O
as	O
opposed	O
to	O
just	O
a	O
theoretical	O
logic	B-Language
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
above	O
pair	O
of	O
sentences	O
look	O
like	O
this	O
in	O
Flora-2	B-Language
:	O
</s>
<s>
Here	O
is	O
default	O
negation	O
(	O
"	O
naf	O
"	O
stands	O
for	O
Negation	B-Application
as	I-Application
failure	I-Application
,	O
based	O
on	O
the	O
well-founded	B-Application
semantics	I-Application
)	O
;	O
Flora-2	B-Language
also	O
supports	O
so-called	O
explicit	O
negation	O
,	O
which	O
is	O
closer	O
to	O
negation	O
in	O
classical	O
logic	B-Language
.	O
</s>
<s>
Flora-2	B-Language
is	O
an	O
extension	O
of	O
F-logic	B-Language
with	O
HiLog	B-Language
,	O
Transaction	B-Language
logic	I-Language
,	O
and	O
defeasible	O
reasoning	O
.	O
</s>
<s>
is	O
a	O
commercial	O
system	O
based	O
on	O
F-logic	B-Language
,	O
which	O
extends	O
Flora-2	B-Language
.	O
</s>
<s>
is	O
a	O
full	O
logic	B-Language
programming	I-Language
language	I-Language
based	O
on	O
F-logic	B-Language
.	O
</s>
<s>
ObjectLogic	O
language	O
is	O
based	O
on	O
F-logic	B-Language
;	O
OntoStudio	O
is	O
an	O
ObjectLogic	O
implementation	O
by	O
semafora	O
systems	O
GmbH	O
(	O
formerly	O
Ontoprise	O
GmbH	O
)	O
.	O
</s>
<s>
OO-logic	O
is	O
a	O
successor	O
of	O
F-logic	B-Language
;	O
SemReasoner	O
and	O
Ontology	B-Language
Management	O
System	O
(	O
OSM	O
)	O
are	O
implementations	O
of	O
OO-logic	O
by	O
adesso	O
SE	O
.	O
</s>
