<s>
In	O
text	B-Algorithm
retrieval	I-Algorithm
,	O
full-text	B-Application
search	I-Application
refers	O
to	O
techniques	O
for	O
searching	O
a	O
single	O
computer-stored	O
document	O
or	O
a	O
collection	O
in	O
a	O
full-text	B-Application
database	O
.	O
</s>
<s>
Full-text	B-Application
search	I-Application
is	O
distinguished	O
from	O
searches	O
based	O
on	O
metadata	O
or	O
on	O
parts	O
of	O
the	O
original	O
texts	O
represented	O
in	O
databases	O
(	O
such	O
as	O
titles	O
,	O
abstracts	O
,	O
selected	O
sections	O
,	O
or	O
bibliographical	O
references	O
)	O
.	O
</s>
<s>
In	O
a	O
full-text	B-Application
search	I-Application
,	O
a	O
search	B-Application
engine	I-Application
examines	O
all	O
of	O
the	O
words	O
in	O
every	O
stored	O
document	O
as	O
it	O
tries	O
to	O
match	O
search	B-Application
criteria	I-Application
(	O
for	O
example	O
,	O
text	O
specified	O
by	O
a	O
user	O
)	O
.	O
</s>
<s>
Full-text-searching	O
techniques	O
became	O
common	O
in	O
online	O
bibliographic	B-Library
databases	I-Library
in	O
the	O
1990s	O
.	O
</s>
<s>
Many	O
websites	O
and	O
application	O
programs	O
(	O
such	O
as	O
word	B-General_Concept
processing	I-General_Concept
software	O
)	O
provide	O
full-text-search	O
capabilities	O
.	O
</s>
<s>
Some	O
web	B-Application
search	I-Application
engines	I-Application
,	O
such	O
as	O
AltaVista	O
,	O
employ	O
full-text-search	O
techniques	O
,	O
while	O
others	O
index	B-Application
only	O
a	O
portion	O
of	O
the	O
web	O
pages	O
examined	O
by	O
their	O
indexing	O
systems	O
.	O
</s>
<s>
When	O
dealing	O
with	O
a	O
small	O
number	O
of	O
documents	O
,	O
it	O
is	O
possible	O
for	O
the	O
full-text-search	O
engine	O
to	O
directly	O
scan	O
the	O
contents	O
of	O
the	O
documents	O
with	O
each	O
query	B-Library
,	O
a	O
strategy	O
called	O
"	O
serial	O
scanning	O
"	O
.	O
</s>
<s>
This	O
is	O
what	O
some	O
tools	O
,	O
such	O
as	O
grep	B-Application
,	O
do	O
when	O
searching	O
.	O
</s>
<s>
However	O
,	O
when	O
the	O
number	O
of	O
documents	O
to	O
search	O
is	O
potentially	O
large	O
,	O
or	O
the	O
quantity	O
of	O
search	O
queries	B-Library
to	O
perform	O
is	O
substantial	O
,	O
the	O
problem	O
of	O
full-text	B-Application
search	I-Application
is	O
often	O
divided	O
into	O
two	O
tasks	O
:	O
indexing	O
and	O
searching	O
.	O
</s>
<s>
The	O
indexing	O
stage	O
will	O
scan	O
the	O
text	O
of	O
all	O
the	O
documents	O
and	O
build	O
a	O
list	O
of	O
search	O
terms	O
(	O
often	O
called	O
an	O
index	B-Application
,	O
but	O
more	O
correctly	O
named	O
a	O
concordance	O
)	O
.	O
</s>
<s>
In	O
the	O
search	O
stage	O
,	O
when	O
performing	O
a	O
specific	O
query	B-Library
,	O
only	O
the	O
index	B-Application
is	O
referenced	O
,	O
rather	O
than	O
the	O
text	O
of	O
the	O
original	O
documents	O
.	O
</s>
<s>
The	O
indexer	O
will	O
make	O
an	O
entry	O
in	O
the	O
index	B-Application
for	O
each	O
term	O
or	O
word	O
found	O
in	O
a	O
document	O
,	O
and	O
possibly	O
note	O
its	O
relative	O
position	O
within	O
the	O
document	O
.	O
</s>
<s>
Some	O
indexers	O
also	O
employ	O
language-specific	O
stemming	B-General_Concept
on	O
the	O
words	O
being	O
indexed	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
words	O
"	O
drives	O
"	O
,	O
"	O
drove	O
"	O
,	O
and	O
"	O
driven	O
"	O
will	O
be	O
recorded	O
in	O
the	O
index	B-Application
under	O
the	O
single	O
concept	O
word	O
"	O
drive	O
"	O
.	O
</s>
<s>
In	O
the	O
diagram	O
the	O
red	O
and	O
green	O
dots	O
represent	O
the	O
total	O
population	O
of	O
potential	O
search	B-Application
results	I-Application
for	O
a	O
given	O
search	O
.	O
</s>
<s>
Relevancy	O
is	O
indicated	O
by	O
the	O
proximity	O
of	O
search	B-Application
results	I-Application
to	O
the	O
center	O
of	O
the	O
inner	O
circle	O
.	O
</s>
<s>
Due	O
to	O
the	O
ambiguities	O
of	O
natural	O
language	O
,	O
full-text-search	O
systems	O
typically	O
includes	O
options	O
like	O
stop	O
words	O
to	O
increase	O
precision	O
and	O
stemming	B-General_Concept
to	O
increase	O
recall	O
.	O
</s>
<s>
Controlled-vocabulary	O
searching	O
also	O
helps	O
alleviate	O
low-precision	O
issues	O
by	O
tagging	B-General_Concept
documents	O
in	O
such	O
a	O
way	O
that	O
ambiguities	O
are	O
eliminated	O
.	O
</s>
<s>
Full-text	B-Application
searching	I-Application
is	O
likely	O
to	O
retrieve	O
many	O
documents	O
that	O
are	O
not	O
relevant	O
to	O
the	O
intended	O
search	O
question	O
.	O
</s>
<s>
The	O
deficiencies	O
of	O
full	B-Application
text	I-Application
searching	O
have	O
been	O
addressed	O
in	O
two	O
ways	O
:	O
By	O
providing	O
users	O
with	O
tools	O
that	O
enable	O
them	O
to	O
express	O
their	O
search	O
questions	O
more	O
precisely	O
,	O
and	O
by	O
developing	O
new	O
search	B-Application
algorithms	I-Application
that	O
improve	O
retrieval	O
precision	O
.	O
</s>
<s>
Keywords	O
improve	O
recall	O
,	O
particularly	O
if	O
the	B-Application
keyword	I-Application
list	O
includes	O
a	O
search	O
word	O
that	O
is	O
not	O
in	O
the	O
document	O
text	O
.	O
</s>
<s>
Field-restricted	O
search	O
.	O
</s>
<s>
Some	O
search	B-Application
engines	I-Application
enable	O
users	O
to	O
limit	O
full	B-Application
text	I-Application
searches	I-Application
to	O
a	O
particular	O
field	B-Application
within	O
a	O
stored	O
data	O
record	O
,	O
such	O
as	O
"	O
Title	O
"	O
or	O
"	O
Author.	O
"	O
</s>
<s>
Searches	O
that	O
use	O
Boolean	O
operators	O
(	O
for	O
example	O
,	O
)	O
can	O
dramatically	O
increase	O
the	O
precision	O
of	O
a	O
full	B-Application
text	I-Application
search	I-Application
.	O
</s>
<s>
Phrase	B-Algorithm
search	I-Algorithm
.	O
</s>
<s>
Proximity	B-Application
search	I-Application
.	O
</s>
<s>
A	O
phrase	B-Algorithm
search	I-Algorithm
matches	O
only	O
those	O
documents	O
that	O
contain	O
two	O
or	O
more	O
words	O
that	O
are	O
separated	O
by	O
a	O
specified	O
number	O
of	O
words	O
;	O
a	O
search	O
for	O
would	O
retrieve	O
only	O
those	O
documents	O
in	O
which	O
the	O
words	O
occur	O
within	O
two	O
words	O
of	O
each	O
other	O
.	O
</s>
<s>
Regular	B-Language
expression	I-Language
.	O
</s>
<s>
A	O
regular	B-Language
expression	I-Language
employs	O
a	O
complex	O
but	O
powerful	O
querying	O
syntax	B-Application
that	O
can	O
be	O
used	O
to	O
specify	O
retrieval	O
conditions	O
with	O
precision	O
.	O
</s>
<s>
Wildcard	B-Algorithm
search	I-Algorithm
.	O
</s>
<s>
A	O
search	O
that	O
substitutes	O
one	O
or	O
more	O
characters	O
in	O
a	O
search	O
query	B-Library
for	O
a	O
wildcard	B-Algorithm
character	I-Algorithm
such	O
as	O
an	O
asterisk	B-Language
.	O
</s>
<s>
For	O
example	O
,	O
using	O
the	O
asterisk	B-Language
in	O
a	O
search	O
query	B-Library
will	O
find	O
"	O
sin	O
"	O
,	O
"	O
son	O
"	O
,	O
"	O
sun	O
"	O
,	O
etc	O
.	O
</s>
<s>
The	O
PageRank	B-Algorithm
algorithm	I-Algorithm
developed	O
by	O
Google	B-Application
gives	O
more	O
prominence	O
to	O
documents	O
to	O
which	O
other	O
Web	O
pages	O
have	O
linked	O
.	O
</s>
<s>
See	O
Search	B-Application
engine	I-Application
for	O
additional	O
examples	O
.	O
</s>
<s>
The	O
following	O
is	O
a	O
partial	O
list	O
of	O
available	O
software	O
products	O
whose	O
predominant	O
purpose	O
is	O
to	O
perform	O
full-text	B-Application
indexing	O
and	O
searching	O
.	O
</s>
<s>
Some	O
of	O
these	O
are	O
accompanied	O
with	O
detailed	O
descriptions	O
of	O
their	O
theory	O
of	O
operation	O
or	O
internal	O
algorithms	O
,	O
which	O
can	O
provide	O
additional	O
insight	O
into	O
how	O
full-text	B-Application
search	I-Application
may	O
be	O
accomplished	O
.	O
</s>
