<s>
A	O
search	B-Application
engine	I-Application
is	O
an	O
information	O
retrieval	O
software	O
program	O
that	O
discovers	O
,	O
crawls	O
,	O
transforms	O
and	O
stores	O
information	O
for	O
retrieval	O
and	O
presentation	O
in	O
response	O
to	O
user	O
queries	O
.	O
</s>
<s>
A	O
search	B-Application
engine	I-Application
normally	O
consists	O
of	O
four	O
components	O
,	O
as	O
follows	O
:	O
a	O
search	O
interface	O
,	O
a	O
crawler	O
(	O
also	O
known	O
as	O
a	O
spider	O
or	O
bot	O
)	O
,	O
an	O
indexer	O
,	O
and	O
a	O
database	O
.	O
</s>
<s>
The	O
crawler	O
traverses	O
a	O
document	O
collection	O
,	O
deconstructs	O
document	O
text	O
,	O
assigns	O
surrogates	O
for	O
storage	O
in	O
the	O
search	B-Application
engine	I-Application
index	O
.	O
</s>
<s>
Online	O
search	B-Application
engines	I-Application
store	O
images	O
,	O
link	O
data	O
and	O
metadata	O
for	O
the	O
document	O
as	O
well	O
.	O
</s>
<s>
He	O
named	O
this	O
device	O
a	O
memex	B-General_Concept
.	O
</s>
<s>
This	O
is	O
the	O
essential	O
feature	O
of	O
the	O
memex	B-General_Concept
.	O
</s>
<s>
All	O
of	O
the	O
documents	O
used	O
in	O
the	O
memex	B-General_Concept
would	O
be	O
in	O
the	O
form	O
of	O
microfilm	O
copy	O
acquired	O
as	O
such	O
or	O
,	O
in	O
the	O
case	O
of	O
personal	O
records	O
,	O
transformed	O
to	O
microfilm	O
by	O
the	O
machine	O
itself	O
.	O
</s>
<s>
Memex	B-General_Concept
would	O
also	O
employ	O
new	O
retrieval	O
techniques	O
based	O
on	O
a	O
new	O
kind	O
of	O
associative	O
indexing	O
the	O
basic	O
idea	O
of	O
which	O
is	O
a	O
provision	O
whereby	O
any	O
item	O
may	O
be	O
caused	O
at	O
will	O
to	O
select	O
immediately	O
and	O
automatically	O
another	O
to	O
create	O
personal	O
"	O
trails	O
"	O
through	O
linked	O
documents	O
.	O
</s>
<s>
In	O
his	O
1967	O
essay	O
titled	O
"	O
Memex	B-General_Concept
Revisited	O
"	O
,	O
he	O
pointed	O
out	O
that	O
the	O
development	O
of	O
the	O
digital	O
computer	O
,	O
the	O
transistor	O
,	O
the	O
video	O
,	O
and	O
other	O
similar	O
devices	O
had	O
heightened	O
the	O
feasibility	O
of	O
such	O
mechanization	O
,	O
but	O
costs	O
would	O
delay	O
its	O
achievements	O
.	O
</s>
<s>
In	O
1987	O
an	O
article	O
was	O
published	O
detailing	O
the	O
development	O
of	O
a	O
character	O
string	O
search	B-Application
engine	I-Application
(	O
SSE	O
)	O
for	O
rapid	O
text	O
retrieval	O
on	O
a	O
double-metal	O
1.6-μm	O
n-well	O
CMOS	O
solid-state	O
circuit	O
with	O
217,600	O
transistors	O
lain	O
out	O
on	O
a	O
8.62x12.76-mm	O
die	O
area	O
.	O
</s>
<s>
Search	B-Application
engines	I-Application
that	O
are	O
expressly	O
designed	O
for	O
searching	O
web	O
pages	O
,	O
documents	O
,	O
and	O
images	O
were	O
developed	O
to	O
facilitate	O
searching	O
through	O
a	O
large	O
,	O
nebulous	O
blob	O
of	O
unstructured	O
resources	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
a	O
wholly	O
textual	O
search	O
,	O
the	O
first	O
step	O
in	O
classifying	O
web	O
pages	O
is	O
to	O
find	O
an	O
‘	O
index	O
item’	O
that	O
might	O
relate	O
expressly	O
to	O
the	O
‘	O
search	O
term.	O
’	O
In	O
the	O
past	O
,	O
search	B-Application
engines	I-Application
began	O
with	O
a	O
small	O
list	O
of	O
URLs	O
as	O
a	O
so-called	O
seed	O
list	O
,	O
fetched	O
the	O
content	O
,	O
and	O
parsed	O
the	O
links	O
on	O
those	O
pages	O
for	O
relevant	O
information	O
,	O
which	O
subsequently	O
provided	O
new	O
links	O
.	O
</s>
<s>
Most	O
search	B-Application
engines	I-Application
use	O
sophisticated	O
scheduling	O
algorithms	O
to	O
“	O
decide	O
”	O
when	O
to	O
revisit	O
a	O
particular	O
page	O
,	O
to	O
appeal	O
to	O
its	O
relevance	O
.	O
</s>
<s>
One	O
such	O
algorithm	O
,	O
PageRank	B-Algorithm
,	O
proposed	O
by	O
Google	O
founders	O
Larry	O
Page	O
and	O
Sergey	O
Brin	O
,	O
is	O
well	O
known	O
and	O
has	O
attracted	O
a	O
lot	O
of	O
attention	O
because	O
it	O
highlights	O
repeat	O
mundanity	O
of	O
web	B-Application
searches	I-Application
courtesy	O
of	O
students	O
that	O
do	O
n't	O
know	O
how	O
to	O
properly	O
research	O
subjects	O
on	O
Google	O
.	O
</s>
<s>
The	O
idea	O
of	O
doing	O
link	O
analysis	O
to	O
compute	O
a	O
popularity	O
rank	O
is	O
older	O
than	O
PageRank	B-Algorithm
.	O
</s>
<s>
However	O
,	O
In	O
October	O
2014	O
,	O
Google	O
’s	O
John	O
Mueller	O
confirmed	O
that	O
Google	O
is	O
not	O
going	O
to	O
be	O
updating	O
it	O
(	O
Page	B-Algorithm
Rank	I-Algorithm
)	O
going	O
forward	O
.	O
</s>
<s>
Search	B-Application
engines	I-Application
often	O
differentiate	O
between	O
internal	O
links	O
and	O
external	O
links	O
,	O
because	O
web	O
masters	O
and	O
mistresses	O
are	O
not	O
strangers	O
to	O
shameless	O
self-promotion	O
.	O
</s>
<s>
Searching	O
for	O
text-based	O
content	O
in	O
databases	O
presents	O
a	O
few	O
special	O
challenges	O
from	O
which	O
a	O
number	O
of	O
specialized	O
search	B-Application
engines	I-Application
flourish	O
.	O
</s>
<s>
Search	B-Application
engine	I-Application
technology	I-Application
has	O
developed	O
to	O
respond	O
to	O
both	O
sets	O
of	O
requirements	O
.	O
</s>
<s>
Most	O
mixed	O
search	B-Application
engines	I-Application
are	O
large	O
Web	B-Application
search	I-Application
engines	I-Application
,	O
like	O
Google	O
.	O
</s>
<s>
They	O
search	O
both	O
through	O
structured	O
and	O
unstructured	B-Application
data	I-Application
sources	O
.	O
</s>
