<s>
Preference	B-General_Concept
learning	I-General_Concept
is	O
a	O
subfield	O
in	O
machine	O
learning	O
,	O
which	O
is	O
a	O
classification	B-General_Concept
method	O
based	O
on	O
observed	O
preference	O
information	O
.	O
</s>
<s>
In	O
the	O
view	O
of	O
supervised	B-General_Concept
learning	I-General_Concept
,	O
preference	B-General_Concept
learning	I-General_Concept
trains	O
on	O
a	O
set	O
of	O
items	O
which	O
have	O
preferences	O
toward	O
labels	O
or	O
other	O
items	O
and	O
predicts	O
the	O
preferences	O
for	O
all	O
items	O
.	O
</s>
<s>
While	O
the	O
concept	O
of	O
preference	B-General_Concept
learning	I-General_Concept
has	O
been	O
emerged	O
for	O
some	O
time	O
in	O
many	O
fields	O
such	O
as	O
economics	O
,	O
it	O
's	O
a	O
relatively	O
new	O
topic	O
in	O
Artificial	B-Application
Intelligence	I-Application
research	I-Application
.	O
</s>
<s>
Several	O
workshops	O
have	O
been	O
discussing	O
preference	B-General_Concept
learning	I-General_Concept
and	O
related	O
topics	O
in	O
the	O
past	O
decade	O
.	O
</s>
<s>
The	O
main	O
task	O
in	O
preference	B-General_Concept
learning	I-General_Concept
concerns	O
problems	O
in	O
"	O
learning	O
to	O
rank	O
"	O
.	O
</s>
<s>
According	O
to	O
different	O
types	O
of	O
preference	O
information	O
observed	O
,	O
the	O
tasks	O
are	O
categorized	O
as	O
three	O
main	O
problems	O
in	O
the	O
book	O
Preference	B-General_Concept
Learning	I-General_Concept
:	O
</s>
<s>
It	O
was	O
observed	O
some	O
conventional	O
classification	B-General_Concept
problems	O
can	O
be	O
generalized	O
in	O
the	O
framework	O
of	O
label	O
ranking	O
problem	O
:	O
if	O
a	O
training	O
instance	O
is	O
labeled	O
as	O
class	O
,	O
it	O
implies	O
that	O
.	O
</s>
<s>
In	O
the	O
multi-label	B-Algorithm
case	O
,	O
is	O
associated	O
with	O
a	O
set	O
of	O
labels	O
and	O
thus	O
the	O
model	O
can	O
extract	O
a	O
set	O
of	O
preference	O
information	O
.	O
</s>
<s>
Training	O
a	O
preference	O
model	O
on	O
this	O
preference	O
information	O
and	O
the	O
classification	B-General_Concept
result	O
of	O
an	O
instance	O
is	O
just	O
the	O
corresponding	O
top	O
ranking	O
label	O
.	O
</s>
<s>
This	O
approach	O
is	O
a	O
natural	O
extension	O
of	O
pairwise	O
classification	B-General_Concept
.	O
</s>
<s>
Preference	B-General_Concept
learning	I-General_Concept
can	O
be	O
used	O
in	O
ranking	O
search	O
results	O
according	O
to	O
feedback	O
of	O
user	O
preference	O
.	O
</s>
<s>
Another	O
application	O
of	O
preference	B-General_Concept
learning	I-General_Concept
is	O
recommender	B-Application
systems	I-Application
.	O
</s>
