<s>
URI	B-Protocol
normalization	I-Protocol
is	O
the	O
process	O
by	O
which	O
URIs	B-Protocol
are	O
modified	O
and	O
standardized	O
in	O
a	O
consistent	O
manner	O
.	O
</s>
<s>
The	O
goal	O
of	O
the	O
normalization	O
process	O
is	O
to	O
transform	O
a	O
URI	B-Protocol
into	O
a	O
normalized	O
URI	B-Protocol
so	O
it	O
is	O
possible	O
to	O
determine	O
if	O
two	O
syntactically	O
different	O
URIs	B-Protocol
may	O
be	O
equivalent	O
.	O
</s>
<s>
Search	B-Application
engines	I-Application
employ	O
URI	B-Protocol
normalization	I-Protocol
in	O
order	O
to	O
correctly	O
rank	O
pages	O
that	O
may	O
be	O
found	O
with	O
multiple	O
URIs	B-Protocol
,	O
and	O
to	O
reduce	O
indexing	O
of	O
duplicate	O
pages	O
.	O
</s>
<s>
Web	B-Application
crawlers	I-Application
perform	O
URI	B-Protocol
normalization	I-Protocol
in	O
order	O
to	O
avoid	O
crawling	O
the	O
same	O
resource	O
more	O
than	O
once	O
.	O
</s>
<s>
Web	B-Application
browsers	I-Application
may	O
perform	O
normalization	O
to	O
determine	O
if	O
a	O
link	O
has	O
been	O
visited	O
or	O
to	O
determine	O
if	O
a	O
page	B-Protocol
has	I-Protocol
been	I-Protocol
cached	I-Protocol
.	O
</s>
<s>
Web	B-Application
servers	I-Application
may	O
also	O
perform	O
normalization	O
for	O
many	O
reasons	O
(	O
i.e.	O
</s>
<s>
The	O
following	O
normalizations	O
are	O
described	O
in	O
RFC	O
3986	O
to	O
result	O
in	O
equivalent	O
URIs	B-Protocol
:	O
</s>
<s>
The	O
hexadecimal	O
digits	O
within	O
a	O
percent-encoding	O
triplet	O
of	O
the	O
URI	B-Protocol
(	O
e.g.	O
,	O
%3a	O
versus	O
%3A	O
)	O
are	O
case-insensitive	O
and	O
therefore	O
should	O
be	O
normalized	O
to	O
use	O
uppercase	O
letters	O
for	O
the	O
digits	O
A-F	O
.	O
</s>
<s>
Converting	O
the	O
scheme	O
and	O
host	B-Device
to	O
lowercase	O
.	O
</s>
<s>
The	O
scheme	O
and	O
host	B-Device
components	O
of	O
the	O
URI	B-Protocol
are	O
case-insensitive	O
and	O
therefore	O
should	O
be	O
normalized	O
to	O
lowercase	O
.	O
</s>
<s>
Percent-encoded	O
triplets	O
of	O
the	O
URI	B-Protocol
in	O
the	O
ranges	O
of	O
ALPHA	O
( %41	O
–	O
%5A	O
and	O
%61	O
–	O
%7A	O
)	O
,	O
DIGIT	O
( %30	O
–	O
%39	O
)	O
,	O
hyphen	O
( %2D	O
)	O
,	O
period	O
( %2E	O
)	O
,	O
underscore	O
( %5F	O
)	O
,	O
or	O
tilde	O
( %7E	O
)	O
do	O
not	O
require	O
percent-encoding	O
and	O
should	O
be	O
decoded	O
to	O
their	O
corresponding	O
unreserved	O
characters	O
.	O
</s>
<s>
and	O
..	O
in	O
the	O
path	O
component	O
of	O
the	O
URI	B-Protocol
should	O
be	O
removed	O
by	O
applying	O
the	O
remove_dot_segments	O
algorithm	O
to	O
the	O
path	O
described	O
in	O
RFC	O
3986	O
.	O
</s>
<s>
Removing	O
the	O
default	B-Protocol
port	I-Protocol
.	O
</s>
<s>
An	O
empty	O
or	O
default	B-Protocol
port	I-Protocol
component	O
of	O
the	O
URI	B-Protocol
(	O
port	O
80	O
for	O
the	O
http	O
scheme	O
)	O
with	O
its	O
"	O
:	O
"	O
delimiter	O
should	O
be	O
removed	O
.	O
</s>
<s>
For	O
http	O
and	O
https	O
URIs	B-Protocol
,	O
the	O
following	O
normalizations	O
listed	O
in	O
RFC	O
3986	O
may	O
result	O
in	O
equivalent	O
URIs	B-Protocol
,	O
but	O
are	O
not	O
guaranteed	O
to	O
by	O
the	O
standards	O
:	O
</s>
<s>
Directories	O
(	O
folders	O
)	O
are	O
indicated	O
with	O
a	O
trailing	O
slash	O
and	O
should	O
be	O
included	O
in	O
URIs	B-Protocol
.	O
</s>
<s>
However	O
,	O
there	O
is	O
no	O
way	O
to	O
know	O
if	O
a	O
URI	B-Protocol
path	O
component	O
represents	O
a	O
directory	O
or	O
not	O
.	O
</s>
<s>
RFC	O
3986	O
notes	O
that	O
if	O
the	O
former	O
URI	B-Protocol
redirects	O
to	O
the	O
latter	O
URI	B-Protocol
,	O
then	O
that	O
is	O
an	O
indication	O
that	O
they	O
are	O
equivalent	O
.	O
</s>
<s>
Applying	O
the	O
following	O
normalizations	O
result	O
in	O
a	O
semantically	O
different	O
URI	B-Protocol
although	O
it	O
may	O
refer	O
to	O
the	O
same	O
resource	O
:	O
</s>
<s>
Default	O
directory	O
indexes	O
are	O
generally	O
not	O
needed	O
in	O
URIs	B-Protocol
.	O
</s>
<s>
The	O
fragment	O
component	O
of	O
a	O
URI	B-Protocol
is	O
never	O
seen	O
by	O
the	O
server	O
and	O
can	O
sometimes	O
be	O
removed	O
.	O
</s>
<s>
However	O
,	O
AJAX	B-General_Concept
applications	O
frequently	O
use	O
the	O
value	O
in	O
the	O
fragment	O
.	O
</s>
<s>
Check	O
if	O
the	O
IP	B-Protocol
address	I-Protocol
maps	O
to	O
a	O
domain	O
name	O
.	O
</s>
<s>
The	O
reverse	O
replacement	O
is	O
rarely	O
safe	O
due	O
to	O
virtual	O
web	B-Application
servers	I-Application
.	O
</s>
<s>
Limiting	O
different	O
application	B-Application
layer	I-Application
protocols	O
.	O
</s>
<s>
A	O
normalizer	O
may	O
determine	O
if	O
one	O
of	O
these	O
URIs	B-Protocol
redirects	O
to	O
the	O
other	O
and	O
normalize	O
all	O
URIs	B-Protocol
appropriately	O
.	O
</s>
<s>
Some	O
web	O
pages	O
use	O
more	O
than	O
one	O
query	O
parameter	O
in	O
the	O
URI	B-Protocol
.	O
</s>
<s>
A	O
normalizer	O
can	O
sort	O
the	O
parameters	O
into	O
alphabetical	O
order	O
(	O
with	O
their	O
values	O
)	O
,	O
and	O
reassemble	O
the	O
URI	B-Protocol
.	O
</s>
<s>
However	O
,	O
the	O
order	O
of	O
parameters	O
in	O
a	O
URI	B-Protocol
may	O
be	O
significant	O
(	O
this	O
is	O
not	O
defined	O
by	O
the	O
standard	O
)	O
and	O
a	O
web	B-Application
server	I-Application
may	O
allow	O
the	O
same	O
variable	O
to	O
appear	O
multiple	O
times	O
.	O
</s>
<s>
Some	O
normalization	O
rules	O
may	O
be	O
developed	O
for	O
specific	O
websites	O
by	O
examining	O
URI	B-Protocol
lists	O
obtained	O
from	O
previous	O
crawls	O
or	O
web	B-Application
server	I-Application
logs	O
.	O
</s>
<s>
we	O
may	O
assume	O
that	O
the	O
two	O
URIs	B-Protocol
are	O
equivalent	O
and	O
can	O
be	O
normalized	O
to	O
one	O
of	O
the	O
URI	B-Protocol
forms	O
.	O
</s>
<s>
(	O
2006	O
)	O
present	O
a	O
heuristic	O
called	O
DustBuster	O
for	O
detecting	O
DUST	O
(	O
different	O
URIs	B-Protocol
with	O
similar	O
text	O
)	O
rules	O
that	O
can	O
be	O
applied	O
to	O
URI	B-Protocol
lists	O
.	O
</s>
<s>
They	O
showed	O
that	O
once	O
the	O
correct	O
DUST	O
rules	O
were	O
found	O
and	O
applied	O
with	O
a	O
normalization	O
algorithm	O
,	O
they	O
were	O
able	O
to	O
find	O
up	O
to	O
68%	O
of	O
the	O
redundant	O
URIs	B-Protocol
in	O
a	O
URI	B-Protocol
list	O
.	O
</s>
