<s>
The	O
Normalized	B-General_Concept
Google	I-General_Concept
Distance	I-General_Concept
(	O
NGD	O
)	O
is	O
a	O
semantic	O
similarity	O
measure	O
derived	O
from	O
the	O
number	O
of	O
hits	O
returned	O
by	O
the	B-Application
Google	I-Application
search	O
engine	O
for	O
a	O
given	O
set	O
of	O
keywords	O
.	O
</s>
<s>
Keywords	O
with	O
the	O
same	O
or	O
similar	O
meanings	O
in	O
a	O
natural	O
language	O
sense	O
tend	O
to	O
be	O
"	O
close	O
"	O
in	O
units	O
of	O
Normalized	B-General_Concept
Google	I-General_Concept
Distance	I-General_Concept
,	O
while	O
words	O
with	O
dissimilar	O
meanings	O
tend	O
to	O
be	O
farther	O
apart	O
.	O
</s>
<s>
where	O
N	O
is	O
the	O
total	O
number	O
of	O
web	O
pages	O
searched	O
by	O
Google	B-Application
multiplied	O
by	O
the	O
average	O
number	O
of	O
singleton	O
search	O
terms	O
occurring	O
on	O
pages	O
;	O
f(x )	O
and	O
f(y )	O
are	O
the	O
number	O
of	O
hits	O
for	O
search	O
terms	O
x	O
and	O
y	O
,	O
respectively	O
;	O
and	O
f(x,y )	O
is	O
the	O
number	O
of	O
web	O
pages	O
on	O
which	O
both	O
x	O
and	O
y	O
occur	O
.	O
</s>
<s>
Example	O
:	O
On	O
9	O
April	O
2013	O
,	O
googling	O
for	O
"	O
Shakespeare	B-Language
"	O
gave	O
130,000,000	O
hits	O
;	O
</s>
<s>
for	O
"	O
Shakespeare	B-Language
Macbeth	O
"	O
gave	O
20,800,000	O
hits	O
.	O
</s>
<s>
very	O
much	O
alike	O
according	O
to	O
the	O
relative	O
semantics	O
supplied	O
by	O
Google	B-Application
.	I-Application
</s>
<s>
The	O
Normalized	B-General_Concept
Google	I-General_Concept
Distance	I-General_Concept
is	O
derived	O
from	O
the	O
earlier	O
Normalized	O
Compression	O
Distance	O
.	O
</s>
<s>
or	O
the	O
literal	O
text	O
of	O
Macbeth	O
by	O
Shakespeare	B-Language
.	O
</s>
<s>
or	O
'	O
the	O
text	O
of	O
Macbeth	O
by	O
Shakespeare.	O
'	O
</s>
<s>
and	O
Google	B-Application
is	O
used	O
.	O
</s>
<s>
Bible	O
or	O
the	B-Application
Oxford	I-Application
English	I-Application
Dictionary	I-Application
together	O
with	O
appropriate	O
search	O
engines	O
.	O
</s>
<s>
For	O
example	O
,	O
"	O
red	O
red	O
"	O
gives	O
about	O
20%	O
more	O
hits	O
of	O
Google	B-Application
on	O
the	O
World	O
Wide	O
Web	O
than	O
"	O
red.	O
"	O
</s>
<s>
From	O
the	O
NGD	O
formula	O
we	O
see	O
that	O
it	O
is	O
symmetric	B-Algorithm
.	O
</s>
<s>
It	O
is	O
hard	O
to	O
come	O
up	O
with	O
practical	O
examples	O
of	O
the	O
World	O
Wide	O
Web	O
using	O
Google	B-Application
that	O
violate	O
the	O
triangle	O
property	O
.	O
</s>
<s>
as	O
well	O
as	O
a	O
randomized	O
massive	O
experiment	O
using	O
WordNet	B-General_Concept
categories	O
.	O
</s>
<s>
and	O
the	B-General_Concept
WordNet	I-General_Concept
experiment	O
the	O
NGD	O
method	O
is	O
augmented	O
with	O
a	O
Support	B-Algorithm
Vector	I-Algorithm
Machine	I-Algorithm
classifier	O
.	O
</s>
<s>
The	B-General_Concept
WordNet	I-General_Concept
experiment	O
consisted	O
of	O
100	O
random	O
WordNet	B-General_Concept
categories	O
.	O
</s>
<s>
These	O
rates	O
are	O
about	O
agreement	O
with	O
the	B-General_Concept
WordNet	I-General_Concept
categories	O
which	O
represent	O
the	O
knowledge	O
of	O
researchers	O
with	O
PhD	O
's	O
which	O
entered	O
them	O
.	O
</s>
