<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
canonicalization	B-General_Concept
(	O
sometimes	O
standardization	O
or	O
normalization	O
)	O
is	O
a	O
process	O
for	O
converting	O
data	O
that	O
has	O
more	O
than	O
one	O
possible	O
representation	O
into	O
a	O
"	O
standard	O
"	O
,	O
"	O
normal	O
"	O
,	O
or	O
canonical	O
form	O
.	O
</s>
<s>
This	O
can	O
be	O
done	O
to	O
compare	O
different	O
representations	O
for	O
equivalence	O
,	O
to	O
count	O
the	O
number	O
of	O
distinct	O
data	O
structures	O
,	O
to	O
improve	O
the	O
efficiency	O
of	O
various	O
algorithms	O
by	O
eliminating	O
repeated	O
calculations	O
,	O
or	O
to	O
make	O
it	O
possible	O
to	O
impose	O
a	O
meaningful	O
sorting	B-Algorithm
order	O
.	O
</s>
<s>
Files	O
in	O
file	B-Application
systems	I-Application
may	O
in	O
most	O
cases	O
be	O
accessed	O
through	O
multiple	O
filenames	B-Device
.	O
</s>
<s>
For	O
instance	O
in	O
Unix-like	O
systems	O
,	O
the	O
string	O
"	O
/./	O
"	O
can	O
be	O
replaced	O
by	O
"	O
/	O
"	O
.	O
</s>
<s>
In	O
the	B-Language
C	I-Language
standard	I-Language
library	I-Language
,	O
the	O
function	O
realpath( )	O
performs	O
this	O
task	O
.	O
</s>
<s>
Other	O
operations	O
performed	O
by	O
this	O
function	O
to	O
canonicalize	B-General_Concept
filenames	B-Device
are	O
the	O
handling	O
of	O
/..	O
components	O
referring	O
to	O
parent	O
directories	O
,	O
simplification	O
of	O
sequences	O
of	O
multiple	O
slashes	O
,	O
removal	O
of	O
trailing	O
slashes	O
,	O
and	O
the	O
resolution	O
of	O
symbolic	B-Application
links	I-Application
.	O
</s>
<s>
Canonicalization	B-General_Concept
of	O
filenames	B-Device
is	O
important	O
for	O
computer	O
security	O
.	O
</s>
<s>
Permitting	O
cmd.exe	O
to	O
execute	O
would	O
be	O
an	O
error	O
caused	O
by	O
a	O
failure	O
to	O
canonicalize	B-General_Concept
the	O
filename	B-Device
to	O
the	O
simplest	O
representation	O
,	O
C:\Windows\System32\cmd.exe,	O
and	O
is	O
called	O
a	O
directory	B-Protocol
traversal	I-Protocol
vulnerability	O
.	O
</s>
<s>
In	O
this	O
context	O
,	O
canonicalization	B-General_Concept
is	O
Unicode	O
normalization	O
.	O
</s>
<s>
Variable-width	O
encodings	O
in	O
the	O
Unicode	O
standard	O
,	O
in	O
particular	O
UTF-8	O
,	O
may	O
cause	O
an	O
additional	O
need	O
for	O
canonicalization	B-General_Concept
in	O
some	O
situations	O
.	O
</s>
<s>
Therefore	O
,	O
if	O
one	O
wants	O
to	O
apply	O
some	O
filter	O
(	O
e	O
.	O
g	O
.	O
a	O
regular	O
expression	O
written	O
in	O
UTF-8	O
)	O
to	O
UTF-8	O
strings	O
that	O
will	O
later	O
be	O
passed	O
to	O
a	O
decoder	O
that	O
allows	O
invalid	O
byte	O
sequences	O
,	O
one	O
should	O
canonicalize	B-General_Concept
the	O
strings	O
before	O
passing	O
them	O
to	O
the	O
filter	O
.	O
</s>
<s>
In	O
this	O
context	O
,	O
canonicalization	B-General_Concept
is	O
the	O
process	O
of	O
translating	O
every	O
string	O
character	O
to	O
its	O
single	O
valid	O
byte	O
sequence	O
.	O
</s>
<s>
An	O
alternative	O
to	O
canonicalization	B-General_Concept
is	O
to	O
reject	O
any	O
strings	O
containing	O
invalid	O
byte	O
sequences	O
.	O
</s>
<s>
A	O
canonical	O
URL	O
is	O
a	O
URL	O
for	O
defining	O
the	O
single	B-Application
source	I-Application
of	I-Application
truth	I-Application
for	O
duplicate	O
content	O
.	O
</s>
<s>
Note	O
that	O
the	O
pages	O
do	O
not	O
need	O
to	O
be	O
absolutely	O
identical	O
;	O
minor	O
changes	O
in	O
sorting	B-Algorithm
or	O
filtering	O
of	O
list	O
pages	O
do	O
not	O
make	O
the	O
page	O
unique	O
(	O
for	O
example	O
,	O
sorting	B-Algorithm
by	O
price	O
or	O
filtering	O
by	O
item	O
color	O
)	O
.	O
</s>
<s>
A	O
canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
can	O
get	O
used	O
to	O
define	O
a	O
canonical	O
URL	O
.	O
</s>
<s>
In	O
intranets	B-General_Concept
,	O
manual	O
searching	O
for	O
information	O
is	O
predominant	O
.	O
</s>
<s>
In	O
web	O
search	O
and	O
search	O
engine	O
optimization	O
(	O
SEO	O
)	O
,	O
URL	B-General_Concept
canonicalization	I-General_Concept
deals	O
with	O
web	O
content	O
that	O
has	O
more	O
than	O
one	O
possible	O
URL	O
.	O
</s>
<s>
Most	O
search	O
engines	O
support	O
the	O
Canonical	B-General_Concept
link	I-General_Concept
element	I-General_Concept
as	O
a	O
hint	O
to	O
which	O
URL	O
should	O
be	O
treated	O
as	O
the	O
true	O
version	O
.	O
</s>
<s>
Briefly	O
,	O
canonicalization	B-General_Concept
removes	O
whitespace	O
within	O
tags	O
,	O
uses	O
particular	O
character	O
encodings	O
,	O
sorts	O
namespace	O
references	O
and	O
eliminates	O
redundant	O
ones	O
,	O
removes	O
XML	O
and	O
DOCTYPE	O
declarations	O
,	O
and	O
transforms	O
relative	O
URIs	O
into	O
absolute	O
URIs	O
.	O
</s>
<s>
Note	O
that	O
only	O
the	O
spaces	O
within	O
the	O
tags	O
are	O
removed	O
under	O
W3C	O
canonicalization	B-General_Concept
,	O
not	O
those	O
between	O
tags	O
.	O
</s>
<s>
A	O
full	O
summary	O
of	O
canonicalization	B-General_Concept
changes	O
is	O
listed	O
below	O
:	O
</s>
<s>
Lemmatisation	B-General_Concept
is	O
the	O
process	O
of	O
converting	O
a	O
word	O
to	O
its	O
canonical	O
form	O
.	O
</s>
