<s>
The	O
skyline	B-Language
operator	I-Language
is	O
the	O
subject	O
of	O
an	O
optimization	O
problem	O
,	O
used	O
in	O
a	O
query	O
to	O
filter	O
results	O
from	O
a	O
database	O
to	O
keep	O
only	O
those	O
objects	O
that	O
are	O
not	O
worse	O
than	O
any	O
other	O
.	O
</s>
<s>
This	O
operator	O
is	O
an	O
extension	O
to	O
SQL	B-Language
proposed	O
by	O
Börzsönyi	O
et	O
al	O
.	O
</s>
<s>
A	O
classic	O
example	O
of	O
application	O
of	O
the	O
skyline	B-Language
operator	I-Language
involves	O
selecting	O
a	O
hotel	O
for	O
a	O
holiday	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
skyline	B-Language
operator	I-Language
would	O
only	O
present	O
those	O
hotels	O
that	O
are	O
not	O
worse	O
than	O
any	O
other	O
hotel	O
in	O
both	O
price	O
and	O
distance	O
to	O
the	O
beach	O
.	O
</s>
<s>
To	O
give	O
an	O
example	O
in	O
SQL	B-Language
:	O
Börzsönyi	O
et	O
al	O
.	O
</s>
<s>
proposed	O
the	O
following	O
syntax	O
for	O
the	O
skyline	B-Language
operator	I-Language
:	O
</s>
<s>
The	O
skyline	B-Language
operator	I-Language
can	O
be	O
implemented	O
directly	O
in	O
SQL	B-Language
using	O
current	O
SQL	B-Language
constructs	O
,	O
but	O
this	O
has	O
been	O
shown	O
to	O
be	O
very	O
slow	O
.	O
</s>
<s>
Other	O
algorithms	O
have	O
been	O
proposed	O
that	O
make	O
use	O
of	O
divide	O
and	O
conquer	O
,	O
indices	O
,	O
MapReduce	B-Operating_System
and	O
general-purpose	B-Architecture
computing	I-Architecture
on	I-Architecture
graphics	I-Architecture
cards	I-Architecture
.	O
</s>
