<s>
The	O
Rule	B-Language
Interchange	I-Language
Format	I-Language
(	O
RIF	O
)	O
is	O
a	O
W3C	O
Recommendation	O
.	O
</s>
<s>
RIF	O
is	O
part	O
of	O
the	O
infrastructure	O
for	O
the	O
semantic	O
web	O
,	O
along	O
with	O
(	O
principally	O
)	O
SPARQL	B-Language
,	O
RDF	O
and	O
OWL	B-Language
.	O
</s>
<s>
A	O
rule	O
system	O
is	O
an	O
implementation	O
of	O
a	O
particular	O
syntax	B-Application
and	O
semantics	B-Application
of	O
rules	O
,	O
which	O
may	O
extend	O
the	O
simple	O
notion	O
described	O
above	O
to	O
include	O
existential	B-Algorithm
quantification	I-Algorithm
,	O
disjunction	O
,	O
logical	O
conjunction	O
,	O
negation	O
,	O
functions	O
,	O
non	O
monotonicity	O
,	O
and	O
many	O
other	O
features	O
.	O
</s>
<s>
Rule	O
systems	O
have	O
been	O
implemented	O
and	O
studied	O
since	O
the	O
mid-1970s	O
and	O
saw	O
significant	O
uptake	O
in	O
the	O
1980s	O
during	O
the	O
height	O
of	O
so-called	O
Expert	B-Application
Systems	I-Application
.	O
</s>
<s>
Some	O
of	O
the	O
datatypes	O
are	O
adapted	O
from	O
XML	O
Schema	O
Datatypes	O
,	O
XPath	B-Language
functions	O
and	O
rdf:PlainLiteral	O
functions	O
.	O
</s>
<s>
Framework	O
for	O
Logic	O
Dialects	O
(	O
FLD	O
)	O
describes	O
mechanisms	O
for	O
specifying	O
the	O
syntax	B-Application
and	O
semantics	B-Application
of	O
logic	O
RIF	O
dialects	O
,	O
including	O
the	O
RIF-BLD	O
and	O
RIF-Core	O
,	O
but	O
not	O
RIF-PRD	O
which	O
is	O
not	O
a	O
logic-based	O
RIF	O
dialect	O
.	O
</s>
<s>
RIF-BLD	O
has	O
a	O
model-theoretic	O
semantics	B-Application
.	O
</s>
<s>
The	O
frame	O
syntax	B-Application
of	O
RIF	O
BLD	O
is	O
based	O
on	O
F-logic	B-Language
,	O
but	O
RIF	O
BLD	O
does	O
n't	O
have	O
the	O
non-monotonic	O
reasoning	O
features	O
of	O
F-logic	B-Language
.	O
</s>
<s>
RIF-PRD	O
has	O
an	O
operational	O
semantics	B-Application
,	O
whereas	O
the	O
condition	O
formulas	O
also	O
have	O
a	O
model-theoretic	O
semantics	B-Application
.	O
</s>
<s>
The	O
Core	O
Answer	B-Application
Set	I-Application
Programming	I-Application
Dialect	O
(	O
CASPD	O
)	O
is	O
based	O
on	O
answer	B-Application
set	I-Application
programming	I-Application
,	O
that	O
is	O
,	O
declarative	O
logic	O
programming	O
based	O
on	O
the	O
answer	B-Application
set	I-Application
semantics	I-Application
(	O
stable	B-Application
model	I-Application
semantics	I-Application
)	O
.	O
</s>
<s>
RIF-SILK	O
can	O
be	O
used	O
to	O
model	O
default	B-Application
logic	I-Application
.	O
</s>
<s>
It	O
is	O
based	O
on	O
declarative	O
logic	O
programming	O
with	O
the	O
well-founded	B-Application
semantics	I-Application
.	O
</s>
