<s>
The	O
Web	B-Language
Ontology	I-Language
Language	I-Language
(	O
OWL	B-Language
)	O
is	O
a	O
family	O
of	O
knowledge	O
representation	O
languages	O
for	O
authoring	O
ontologies	O
.	O
</s>
<s>
Ontologies	O
resemble	O
class	B-Application
hierarchies	I-Application
in	O
object-oriented	B-Language
programming	I-Language
but	O
there	O
are	O
several	O
critical	O
differences	O
.	O
</s>
<s>
Class	B-Application
hierarchies	I-Application
are	O
meant	O
to	O
represent	O
structures	O
used	O
in	O
source	O
code	O
that	O
evolve	O
fairly	O
slowly	O
(	O
perhaps	O
with	O
monthly	O
revisions	O
)	O
whereas	O
ontologies	O
are	O
meant	O
to	O
represent	O
information	O
on	O
the	O
Internet	O
and	O
are	O
expected	O
to	O
be	O
evolving	O
almost	O
constantly	O
.	O
</s>
<s>
Class	B-Application
hierarchies	I-Application
on	O
the	O
other	O
hand	O
tend	O
to	O
be	O
fairly	O
static	O
and	O
rely	O
on	O
far	O
less	O
diverse	O
and	O
more	O
structured	O
sources	O
of	O
data	O
such	O
as	O
corporate	O
databases	O
.	O
</s>
<s>
The	O
OWL	B-Language
languages	O
are	O
characterized	O
by	O
formal	B-Application
semantics	I-Application
.	O
</s>
<s>
OWL	B-Language
and	O
RDF	O
have	O
attracted	O
significant	O
academic	O
,	O
medical	O
and	O
commercial	O
interest	O
.	O
</s>
<s>
In	O
October	O
2007	O
,	O
a	O
new	O
W3C	O
working	O
group	O
was	O
started	O
to	O
extend	O
OWL	B-Language
with	O
several	O
new	O
features	O
as	O
proposed	O
in	O
the	O
OWL	B-Language
1.1	O
member	O
submission	O
.	O
</s>
<s>
W3C	O
announced	O
the	O
new	O
version	O
of	O
OWL	B-Language
on	O
27	O
October	O
2009	O
.	O
</s>
<s>
This	O
new	O
version	O
,	O
called	O
OWL	B-Language
2	I-Language
,	O
soon	O
found	O
its	O
way	O
into	O
semantic	O
editors	O
such	O
as	O
Protégé	B-Language
and	O
semantic	O
reasoners	O
such	O
as	O
Pellet	B-Language
,	O
RacerPro	B-Language
,	O
FaCT++	B-Language
and	O
HermiT	O
.	O
</s>
<s>
The	O
OWL	B-Language
family	O
contains	O
many	O
species	O
,	O
serializations	B-Application
,	O
syntaxes	O
and	O
specifications	O
with	O
similar	O
names	O
.	O
</s>
<s>
OWL	B-Language
and	O
OWL2	O
are	O
used	O
to	O
refer	O
to	O
the	O
2004	O
and	O
2009	O
specifications	O
,	O
respectively	O
.	O
</s>
<s>
When	O
referring	O
more	O
generally	O
,	O
OWL	B-Language
Family	O
will	O
be	O
used	O
.	O
</s>
<s>
Since	O
the	O
1990s	O
,	O
a	O
number	O
of	O
research	O
efforts	O
have	O
explored	O
how	O
the	O
idea	O
of	O
knowledge	O
representation	O
(	O
KR	O
)	O
from	O
artificial	B-Application
intelligence	I-Application
(	O
AI	B-Application
)	O
could	O
be	O
made	O
useful	O
on	O
the	O
World	O
Wide	O
Web	O
.	O
</s>
<s>
These	O
included	O
languages	O
based	O
on	O
HTML	B-Language
(	O
called	O
SHOE	B-General_Concept
)	O
,	O
based	O
on	O
XML	B-Protocol
(	O
called	O
XOL	O
,	O
later	O
OIL	B-Language
)	O
,	O
and	O
various	O
frame-based	O
KR	O
languages	O
and	O
knowledge	O
acquisition	O
approaches	O
.	O
</s>
<s>
In	O
2000	O
in	O
the	O
United	O
States	O
,	O
DARPA	O
started	O
development	O
of	O
DAML	B-Language
led	O
by	O
James	O
Hendler	O
.	O
</s>
<s>
In	O
March	O
2001	O
,	O
the	O
Joint	O
EU/US	O
Committee	O
on	O
Agent	O
Markup	O
Languages	O
decided	O
that	O
DAML	B-Language
should	O
be	O
merged	O
with	O
OIL	B-Language
.	O
</s>
<s>
The	O
EU/US	O
ad	O
hoc	O
Joint	O
Working	O
Group	O
on	O
Agent	O
Markup	O
Languages	O
was	O
convened	O
to	O
develop	O
DAML+OIL	O
as	O
a	O
web	B-Language
ontology	I-Language
language	I-Language
.	O
</s>
<s>
This	O
group	O
was	O
jointly	O
funded	O
by	O
the	O
DARPA	O
(	O
under	O
the	O
DAML	B-Language
program	O
)	O
and	O
the	O
European	O
Union	O
's	O
Information	O
Society	O
Technologies	O
(	O
IST	O
)	O
funding	O
project	O
.	O
</s>
<s>
DAML+OIL	O
was	O
intended	O
to	O
be	O
a	O
thin	O
layer	O
above	O
RDFS	O
,	O
</s>
<s>
with	O
formal	B-Application
semantics	I-Application
based	O
on	O
a	O
description	B-Language
logic	I-Language
(	O
DL	O
)	O
.	O
</s>
<s>
DAML+OIL	O
is	O
a	O
particularly	O
major	O
influence	O
on	O
OWL	B-Language
;	O
OWL	B-Language
's	O
design	O
was	O
specifically	O
based	O
on	O
DAML+OIL	O
.	O
</s>
<s>
The	O
first	O
working	O
drafts	O
of	O
the	O
abstract	B-Application
syntax	I-Application
,	O
reference	O
and	O
synopsis	O
were	O
published	O
in	O
July	O
2002	O
.	O
</s>
<s>
OWL	B-Language
became	O
a	O
formal	O
W3C	O
recommendation	O
on	O
February	O
10	O
,	O
2004	O
and	O
the	O
working	O
group	O
was	O
disbanded	O
on	O
May	O
31	O
,	O
2004	O
.	O
</s>
<s>
In	O
2005	O
,	O
at	O
the	O
OWL	B-Language
Experiences	O
And	O
Directions	O
Workshop	O
a	O
consensus	O
formed	O
that	O
recent	O
advances	O
in	O
description	B-Language
logic	I-Language
would	O
allow	O
a	O
more	O
expressive	O
revision	O
to	O
satisfy	O
user	O
requirements	O
more	O
comprehensively	O
whilst	O
retaining	O
good	O
computational	O
properties	O
.	O
</s>
<s>
The	O
W3C	O
chartered	O
the	O
OWL	B-Language
Working	O
Group	O
as	O
part	O
of	O
the	O
Semantic	O
Web	O
Activity	O
in	O
September	O
2007	O
.	O
</s>
<s>
OWL	B-Language
2	I-Language
became	O
a	O
W3C	O
recommendation	O
in	O
October	O
2009	O
.	O
</s>
<s>
OWL	B-Language
2	I-Language
introduces	O
profiles	O
to	O
improve	O
scalability	O
in	O
typical	O
applications	O
.	O
</s>
<s>
OWL	B-Language
was	O
chosen	O
as	O
an	O
easily	O
pronounced	O
acronym	O
that	O
would	O
yield	O
good	O
logos	O
,	O
suggest	O
wisdom	O
,	O
and	O
honor	O
William	O
A	O
.	O
Martin	O
's	O
One	O
World	O
Language	O
knowledge	O
representation	O
project	O
from	O
the	O
1970s	O
.	O
</s>
<s>
A	O
2006	O
survey	O
of	O
ontologies	O
available	O
on	O
the	O
web	O
collected	O
688	O
OWL	B-Language
ontologies	I-Language
.	O
</s>
<s>
Of	O
these	O
,	O
199	O
were	O
OWL	B-Language
Lite	O
,	O
149	O
were	O
OWL	B-Language
DL	O
and	O
337	O
OWL	B-Language
Full	O
(	O
by	O
syntax	O
)	O
.	O
</s>
<s>
The	O
data	O
described	O
by	O
an	O
ontology	O
in	O
the	O
OWL	B-Language
family	O
is	O
interpreted	O
as	O
a	O
set	O
of	O
"	O
individuals	O
"	O
and	O
a	O
set	O
of	O
"	O
property	O
assertions	O
"	O
which	O
relate	O
these	O
individuals	O
to	O
each	O
other	O
.	O
</s>
<s>
An	O
ontology	O
consists	O
of	O
a	O
set	O
of	O
axioms	B-Algorithm
which	O
place	O
constraints	O
on	O
sets	O
of	O
individuals	O
(	O
called	O
"	O
classes	O
"	O
)	O
and	O
the	O
types	O
of	O
relationships	O
permitted	O
between	O
them	O
.	O
</s>
<s>
These	O
axioms	B-Algorithm
provide	O
semantics	B-Application
by	O
allowing	O
systems	O
to	O
infer	O
additional	O
information	O
based	O
on	O
the	O
data	O
explicitly	O
provided	O
.	O
</s>
<s>
A	O
full	O
introduction	O
to	O
the	O
expressive	O
power	O
of	O
the	O
OWL	B-Language
is	O
provided	O
in	O
the	O
W3C	O
's	O
OWL	B-Language
Guide	O
.	O
</s>
<s>
OWL	B-Language
ontologies	I-Language
can	O
import	O
other	O
ontologies	O
,	O
adding	O
information	O
from	O
the	O
imported	O
ontology	O
to	O
the	O
current	O
ontology	O
.	O
</s>
<s>
An	O
ontology	O
describing	O
families	O
might	O
include	O
axioms	B-Algorithm
stating	O
that	O
a	O
"	O
hasMother	O
"	O
property	O
is	O
only	O
present	O
between	O
two	O
individuals	O
when	O
"	O
hasParent	O
"	O
is	O
also	O
present	O
,	O
and	O
that	O
individuals	O
of	O
class	O
"	O
HasTypeOBlood	O
"	O
are	O
never	O
related	O
via	O
"	O
hasParent	O
"	O
to	O
members	O
of	O
the	O
"	O
HasTypeABBlood	O
"	O
class	O
.	O
</s>
<s>
The	O
W3C-endorsed	O
OWL	B-Language
specification	O
includes	O
the	O
definition	O
of	O
three	O
variants	O
of	O
OWL	B-Language
,	O
with	O
different	O
levels	O
of	O
expressiveness	O
.	O
</s>
<s>
These	O
are	O
OWL	B-Language
Lite	O
,	O
OWL	B-Language
DL	O
and	O
OWL	B-Language
Full	O
(	O
ordered	O
by	O
increasing	O
expressiveness	O
)	O
.	O
</s>
<s>
Each	O
of	O
these	O
sublanguages	B-Application
is	O
a	O
syntactic	O
extension	O
of	O
its	O
simpler	O
predecessor	O
.	O
</s>
<s>
Every	O
legal	O
OWL	B-Language
Lite	O
ontology	O
is	O
a	O
legal	O
OWL	B-Language
DL	O
ontology	O
.	O
</s>
<s>
Every	O
legal	O
OWL	B-Language
DL	O
ontology	O
is	O
a	O
legal	O
OWL	B-Language
Full	O
ontology	O
.	O
</s>
<s>
Every	O
valid	O
OWL	B-Language
Lite	O
conclusion	O
is	O
a	O
valid	O
OWL	B-Language
DL	O
conclusion	O
.	O
</s>
<s>
Every	O
valid	O
OWL	B-Language
DL	O
conclusion	O
is	O
a	O
valid	O
OWL	B-Language
Full	O
conclusion	O
.	O
</s>
<s>
OWL	B-Language
Lite	O
was	O
originally	O
intended	O
to	O
support	O
those	O
users	O
primarily	O
needing	O
a	O
classification	O
hierarchy	O
and	O
simple	O
constraints	O
.	O
</s>
<s>
For	O
example	O
,	O
while	O
it	O
supports	O
cardinality	B-Application
constraints	O
,	O
it	O
only	O
permits	O
cardinality	B-Application
values	O
of	O
0	O
or	O
1	O
.	O
</s>
<s>
It	O
was	O
hoped	O
that	O
it	O
would	O
be	O
simpler	O
to	O
provide	O
tool	O
support	O
for	O
OWL	B-Language
Lite	O
than	O
its	O
more	O
expressive	O
relatives	O
,	O
allowing	O
quick	O
migration	O
path	O
for	O
systems	O
using	O
thesauri	O
and	O
other	O
taxonomies	O
.	O
</s>
<s>
In	O
practice	O
,	O
however	O
,	O
most	O
of	O
the	O
expressiveness	O
constraints	O
placed	O
on	O
OWL	B-Language
Lite	O
amount	O
to	O
little	O
more	O
than	O
syntactic	O
inconveniences	O
:	O
most	O
of	O
the	O
constructs	O
available	O
in	O
OWL	B-Language
DL	O
can	O
be	O
built	O
using	O
complex	O
combinations	O
of	O
OWL	B-Language
Lite	O
features	O
,	O
and	O
is	O
equally	O
expressive	O
as	O
the	O
description	B-Language
logic	I-Language
.	O
</s>
<s>
Development	O
of	O
OWL	B-Language
Lite	O
tools	O
has	O
thus	O
proven	O
to	O
be	O
almost	O
as	O
difficult	O
as	O
development	O
of	O
tools	O
for	O
OWL	B-Language
DL	O
,	O
and	O
OWL	B-Language
Lite	O
is	O
not	O
widely	O
used	O
.	O
</s>
<s>
OWL	B-Language
DL	O
is	O
designed	O
to	O
provide	O
the	O
maximum	O
expressiveness	O
possible	O
while	O
retaining	O
computational	O
completeness	O
(	O
either	O
φ	O
or	O
¬φ	O
holds	O
)	O
,	O
decidability	O
(	O
there	O
is	O
an	O
effective	O
procedure	O
to	O
determine	O
whether	O
φ	O
is	O
derivable	O
or	O
not	O
)	O
,	O
and	O
the	O
availability	O
of	O
practical	O
reasoning	O
algorithms	O
.	O
</s>
<s>
OWL	B-Language
DL	O
includes	O
all	O
OWL	B-Language
language	O
constructs	O
,	O
but	O
they	O
can	O
be	O
used	O
only	O
under	O
certain	O
restrictions	O
(	O
for	O
example	O
,	O
number	O
restrictions	O
may	O
not	O
be	O
placed	O
upon	O
properties	O
which	O
are	O
declared	O
to	O
be	O
transitive	O
;	O
and	O
while	O
a	O
class	O
may	O
be	O
a	O
subclass	O
of	O
many	O
classes	O
,	O
a	O
class	O
cannot	O
be	O
an	O
instance	O
of	O
another	O
class	O
)	O
.	O
</s>
<s>
OWL	B-Language
DL	O
is	O
so	O
named	O
due	O
to	O
its	O
correspondence	O
with	O
description	B-Language
logic	I-Language
,	O
a	O
field	O
of	O
research	O
that	O
has	O
studied	O
the	O
logics	O
that	O
form	O
the	O
formal	O
foundation	O
of	O
OWL	B-Language
.	O
</s>
<s>
OWL	B-Language
Full	O
is	O
based	O
on	O
a	O
different	O
semantics	B-Application
from	O
OWL	B-Language
Lite	O
or	O
OWL	B-Language
DL	O
,	O
and	O
was	O
designed	O
to	O
preserve	O
some	O
compatibility	O
with	O
RDF	O
Schema	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
OWL	B-Language
Full	O
a	O
class	O
can	O
be	O
treated	O
simultaneously	O
as	O
a	O
collection	O
of	O
individuals	O
and	O
as	O
an	O
individual	O
in	O
its	O
own	O
right	O
;	O
this	O
is	O
not	O
permitted	O
in	O
OWL	B-Language
DL	O
.	O
</s>
<s>
OWL	B-Language
Full	O
allows	O
an	O
ontology	O
to	O
augment	O
the	O
meaning	O
of	O
the	O
pre-defined	O
(	O
RDF	O
or	O
OWL	B-Language
)	O
vocabulary	O
.	O
</s>
<s>
OWL	B-Language
Full	O
is	O
undecidable	O
,	O
so	O
no	O
reasoning	O
software	O
is	O
able	O
to	O
perform	O
complete	O
reasoning	O
for	O
it	O
.	O
</s>
<s>
In	O
OWL	B-Language
2	I-Language
,	O
there	O
are	O
three	O
sublanguages	B-Application
of	O
the	O
language	O
.	O
</s>
<s>
OWL	B-Language
2	I-Language
EL	O
is	O
a	O
fragment	O
that	O
has	O
polynomial	O
time	O
reasoning	O
complexity	O
;	O
OWL	B-Language
2	I-Language
QL	O
is	O
designed	O
to	O
enable	O
easier	O
access	O
and	O
query	O
to	O
data	O
stored	O
in	O
databases	O
;	O
OWL	B-Language
2	I-Language
RL	O
is	O
a	O
rule	O
subset	O
of	O
OWL	B-Language
2	I-Language
.	O
</s>
<s>
The	O
OWL	B-Language
family	O
of	O
languages	O
supports	O
a	O
variety	O
of	O
syntaxes	O
.	O
</s>
<s>
These	O
are	O
close	O
to	O
the	O
ontology	O
structure	O
of	O
languages	O
in	O
the	O
OWL	B-Language
family	O
.	O
</s>
<s>
High	O
level	O
syntax	O
is	O
used	O
to	O
specify	O
the	O
OWL	B-Language
ontology	I-Language
structure	O
and	O
semantics	B-Application
.	O
</s>
<s>
The	O
OWL	B-Language
abstract	B-Application
syntax	I-Application
presents	O
an	O
ontology	O
as	O
a	O
sequence	O
of	O
annotations	O
,	O
axioms	B-Algorithm
and	O
facts	O
.	O
</s>
<s>
Information	O
about	O
the	O
classes	O
,	O
properties	O
and	O
individuals	O
that	O
compose	O
the	O
ontology	O
is	O
contained	O
in	O
axioms	B-Algorithm
and	O
facts	O
only	O
.	O
</s>
<s>
Each	O
class	O
,	O
property	O
and	O
individual	O
is	O
either	O
anonymous	O
or	O
identified	O
by	O
an	O
URI	B-Protocol
reference	I-Protocol
.	O
</s>
<s>
Axioms	B-Algorithm
specify	O
the	O
characteristics	O
of	O
classes	O
and	O
properties	O
.	O
</s>
<s>
This	O
style	O
is	O
similar	O
to	O
frame	O
languages	O
,	O
and	O
quite	O
dissimilar	O
to	O
well	O
known	O
syntaxes	O
for	O
DLs	B-Language
and	O
Resource	O
Description	O
Framework	O
(	O
RDF	O
)	O
.	O
</s>
<s>
They	O
conclude	O
that	O
the	O
name	O
abstract	B-Application
syntax	I-Application
may	O
be	O
somewhat	O
misleading	O
.	O
</s>
<s>
It	O
is	O
used	O
by	O
OWL2	O
to	O
specify	O
semantics	B-Application
,	O
mappings	O
to	O
exchange	O
syntaxes	O
and	O
profiles	O
.	O
</s>
<s>
for	O
languages	O
in	O
the	O
OWL	B-Language
family	O
.	O
</s>
<s>
Several	O
RDF	O
serialization	B-Application
formats	O
have	O
been	O
devised	O
.	O
</s>
<s>
Each	O
leads	O
to	O
a	O
syntax	O
for	O
languages	O
in	O
the	O
OWL	B-Language
family	O
through	O
this	O
mapping	O
.	O
</s>
<s>
RDF/XML	O
is	O
normative	O
.	O
</s>
<s>
OWL2	O
specifies	O
an	O
XML	B-Protocol
serialization	B-Application
that	O
closely	O
models	O
the	O
structure	O
of	O
an	O
OWL2	O
ontology	O
.	O
</s>
<s>
Variations	O
are	O
available	O
for	O
OWL	B-Language
and	O
OWL2	O
.	O
</s>
<s>
Not	O
all	O
OWL	B-Language
and	O
OWL2	O
ontologies	O
can	O
be	O
expressed	O
in	O
this	O
syntax	O
.	O
</s>
<s>
The	O
W3C	O
OWL	B-Language
2	I-Language
Web	B-Language
Ontology	I-Language
Language	I-Language
provides	O
syntax	O
examples	O
.	O
</s>
<s>
Every	O
OWL	B-Language
ontology	I-Language
must	O
be	O
identified	O
by	O
a	O
URI	B-Protocol
(	O
http://www.example.org/tea.owl	O
,	O
say	O
)	O
.	O
</s>
<s>
OWL	B-Language
classes	O
correspond	O
to	O
description	B-Language
logic	I-Language
(	O
DL	O
)	O
concepts	O
,	O
OWL	B-Language
properties	O
to	O
DL	O
roles	O
,	O
while	O
individuals	O
are	O
called	O
the	O
same	O
way	O
in	O
both	O
the	O
OWL	B-Language
and	O
the	O
DL	O
terminology	O
.	O
</s>
<s>
Members	O
of	O
the	O
OWL	B-Language
family	O
have	O
model	O
theoretic	O
formal	B-Application
semantics	I-Application
,	O
and	O
so	O
have	O
strong	O
logical	O
foundations	O
.	O
</s>
<s>
Description	B-Language
logics	I-Language
are	O
a	O
family	O
of	O
logics	O
that	O
are	O
decidable	O
fragments	O
of	O
first-order	O
logic	O
with	O
attractive	O
and	O
well-understood	O
computational	O
properties	O
.	O
</s>
<s>
OWL	B-Language
DL	O
and	O
OWL	B-Language
Lite	O
semantics	B-Application
are	O
based	O
on	O
DLs	B-Language
.	O
</s>
<s>
They	O
combine	O
a	O
syntax	O
for	O
describing	O
and	O
exchanging	O
ontologies	O
,	O
and	O
formal	B-Application
semantics	I-Application
that	O
gives	O
them	O
meaning	O
.	O
</s>
<s>
For	O
example	O
,	O
OWL	B-Language
DL	O
corresponds	O
to	O
the	O
description	B-Language
logic	I-Language
,	O
while	O
OWL	B-Language
2	I-Language
corresponds	O
to	O
the	O
logic	O
.	O
</s>
<s>
systems	O
which	O
are	O
guaranteed	O
to	O
derive	O
every	O
consequence	O
of	O
the	O
knowledge	O
in	O
an	O
ontology	O
)	O
exist	O
for	O
these	O
DLs	B-Language
.	O
</s>
<s>
OWL	B-Language
Full	O
is	O
intended	O
to	O
be	O
compatible	O
with	O
RDF	O
Schema	O
(	O
RDFS	O
)	O
,	O
and	O
to	O
be	O
capable	O
of	O
augmenting	O
the	O
meanings	O
of	O
existing	O
Resource	O
Description	O
Framework	O
(	O
RDF	O
)	O
vocabulary	O
.	O
</s>
<s>
So	O
,	O
the	O
meaning	O
of	O
OWL	B-Language
Full	O
ontologies	O
are	O
defined	O
by	O
extension	O
of	O
the	O
RDFS	O
meaning	O
,	O
and	O
OWL	B-Language
Full	O
is	O
a	O
semantic	O
extension	O
of	O
RDF	O
.	O
</s>
<s>
The	O
languages	O
in	O
the	O
OWL	B-Language
family	O
use	O
the	O
open	B-Application
world	I-Application
assumption	I-Application
.	O
</s>
<s>
Under	O
the	O
open	B-Application
world	I-Application
assumption	I-Application
,	O
if	O
a	O
statement	O
cannot	O
be	O
proven	O
to	O
be	O
true	O
with	O
current	O
knowledge	O
,	O
we	O
cannot	O
draw	O
the	O
conclusion	O
that	O
the	O
statement	O
is	O
false	O
.	O
</s>
<s>
A	O
relational	B-Application
database	I-Application
consists	O
of	O
sets	O
of	O
tuples	B-Application
with	O
the	O
same	O
attributes	O
.	O
</s>
<s>
SQL	B-Language
is	O
a	O
query	O
and	O
management	O
language	O
for	O
relational	B-Application
databases	I-Application
.	O
</s>
<s>
Prolog	B-Language
is	O
a	O
logical	B-Language
programming	I-Language
language	O
.	O
</s>
<s>
Both	O
use	O
the	O
closed	B-Application
world	I-Application
assumption	I-Application
.	O
</s>
<s>
Languages	O
in	O
the	O
OWL	B-Language
family	O
are	O
capable	O
of	O
creating	O
classes	O
,	O
properties	O
,	O
defining	O
instances	O
and	O
its	O
operations	O
.	O
</s>
<s>
It	O
corresponds	O
to	O
a	O
description	B-Language
logic	I-Language
individual	O
.	O
</s>
<s>
All	O
classes	O
are	O
subclasses	O
of	O
owl:Thing	O
(	O
DL	O
top	O
notated	O
)	O
,	O
the	O
root	O
class	O
.	O
</s>
<s>
All	O
classes	O
are	O
subclassed	O
by	O
owl:Nothing	O
(	O
DL	O
bottom	O
notated	O
)	O
,	O
the	O
empty	O
class	O
.	O
</s>
<s>
No	O
instances	O
are	O
members	O
of	O
owl:Nothing	O
.	O
</s>
<s>
Modelers	O
use	O
owl:Thing	O
and	O
owl:Nothing	O
to	O
assert	O
facts	O
about	O
all	O
or	O
no	O
instances	O
.	O
</s>
<s>
Class	O
and	O
their	O
members	O
can	O
be	O
defined	O
in	O
OWL	B-Language
either	O
by	O
extension	O
or	O
by	O
intension	O
.	O
</s>
<s>
Let	O
's	O
call	O
human	O
the	O
class	O
of	O
all	O
humans	O
in	O
the	O
world	O
is	O
a	O
subclass	O
of	O
owl:thing	O
.	O
</s>
<s>
A	O
property	O
is	O
a	O
characteristic	O
of	O
a	O
class	O
-	O
a	O
directed	O
binary	O
relation	O
that	O
specifies	O
some	O
attribute	B-General_Concept
which	O
is	O
true	O
for	O
instances	O
of	O
that	O
class	O
.	O
</s>
<s>
Datatype	O
properties	O
are	O
relations	O
between	O
instances	O
of	O
classes	O
and	O
RDF	O
literals	O
or	O
XML	B-Protocol
schema	O
datatypes	O
.	O
</s>
<s>
They	O
are	O
formulated	O
using	O
owl:DatatypeProperty	O
type	O
.	O
</s>
<s>
They	O
are	O
formulated	O
using	O
owl:ObjectProperty	O
.	O
</s>
<s>
Languages	O
in	O
the	O
OWL	B-Language
family	O
support	O
various	O
operations	O
on	O
classes	O
such	O
as	O
union	O
,	O
intersection	O
and	O
complement	O
.	O
</s>
<s>
They	O
also	O
allow	O
class	O
enumeration	O
,	O
cardinality	B-Application
,	O
disjointness	B-Algorithm
,	O
and	O
equivalence	O
.	O
</s>
<s>
Metaclasses	B-Language
are	O
classes	O
of	O
classes	O
.	O
</s>
<s>
They	O
are	O
allowed	O
in	O
OWL	B-Language
full	O
or	O
with	O
a	O
feature	O
called	O
class/instance	O
punning	O
.	O
</s>
<s>
This	O
cannot	O
be	O
done	O
within	O
OWL	B-Language
.	O
</s>
<s>
They	O
may	O
need	O
to	O
adopt	O
a	O
pattern	O
instead	O
which	O
encodes	O
the	O
meaning	O
outside	O
the	O
formal	B-Application
semantics	I-Application
.	O
</s>
