<s>
Query	B-Algorithm
expansion	I-Algorithm
(	O
QE	O
)	O
is	O
the	O
process	O
of	O
reformulating	O
a	O
given	O
query	B-Library
to	O
improve	O
retrieval	O
performance	O
in	O
information	B-Library
retrieval	I-Library
operations	O
,	O
particularly	O
in	O
the	O
context	O
of	O
query	B-General_Concept
understanding	I-General_Concept
.	O
</s>
<s>
In	O
the	O
context	O
of	O
search	B-Application
engines	I-Application
,	O
query	B-Algorithm
expansion	I-Algorithm
involves	O
evaluating	O
a	O
user	O
's	O
input	O
(	O
what	O
words	O
were	O
typed	O
into	O
the	O
search	O
query	B-Library
area	O
,	O
and	O
sometimes	O
other	O
types	O
of	O
data	O
)	O
and	O
expanding	O
the	O
search	O
query	B-Library
to	O
match	O
additional	O
documents	O
.	O
</s>
<s>
Query	B-Algorithm
expansion	I-Algorithm
involves	O
techniques	O
such	O
as	O
:	O
</s>
<s>
Query	B-Algorithm
expansion	I-Algorithm
is	O
a	O
methodology	O
studied	O
in	O
the	O
field	O
of	O
computer	B-General_Concept
science	I-General_Concept
,	O
particularly	O
within	O
the	O
realm	O
of	O
natural	B-Language
language	I-Language
processing	I-Language
and	O
information	B-Library
retrieval	I-Library
.	O
</s>
<s>
Search	B-Application
engines	I-Application
invoke	O
query	B-Algorithm
expansion	I-Algorithm
to	O
increase	O
the	O
quality	O
of	O
user	O
search	B-Application
results	I-Application
.	O
</s>
<s>
It	O
is	O
assumed	O
that	O
users	O
do	O
not	O
always	O
formulate	O
search	O
queries	B-Library
using	O
the	O
best	O
terms	O
.	O
</s>
<s>
By	O
stemming	B-General_Concept
a	O
user-entered	O
term	O
,	O
more	O
documents	O
are	O
matched	O
,	O
as	O
the	O
alternate	O
word	O
forms	O
for	O
a	O
user	O
entered	O
term	O
are	O
matched	O
as	O
well	O
,	O
increasing	O
the	O
total	O
recall	O
.	O
</s>
<s>
By	O
expanding	O
a	O
search	O
query	B-Library
to	O
search	O
for	O
the	O
synonyms	B-Application
of	O
a	O
user	O
entered	O
term	O
,	O
the	O
recall	O
is	O
also	O
increased	O
at	O
the	O
expense	O
of	O
precision	O
.	O
</s>
<s>
The	O
goal	O
of	O
query	B-Algorithm
expansion	I-Algorithm
in	O
this	O
regard	O
is	O
by	O
increasing	O
recall	O
,	O
precision	O
can	O
potentially	O
increase	O
(	O
rather	O
than	O
decrease	O
as	O
mathematically	O
equated	O
)	O
,	O
by	O
including	O
in	O
the	O
result	O
set	O
pages	O
which	O
are	O
more	O
relevant	O
(	O
of	O
higher	O
quality	O
)	O
,	O
or	O
at	O
least	O
equally	O
relevant	O
.	O
</s>
<s>
Pages	O
which	O
would	O
not	O
be	O
included	O
in	O
the	O
result	O
set	O
,	O
which	O
have	O
the	O
potential	O
to	O
be	O
more	O
relevant	O
to	O
the	O
user	O
's	O
desired	O
query	B-Library
,	O
are	O
included	O
,	O
and	O
without	O
query	B-Algorithm
expansion	I-Algorithm
would	O
not	O
have	O
,	O
regardless	O
of	O
relevance	O
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
many	O
of	O
the	O
current	O
commercial	O
search	B-Application
engines	I-Application
use	O
word	O
frequency	O
(	O
tf-idf	O
)	O
to	O
assist	O
in	O
ranking	O
.	O
</s>
<s>
By	O
ranking	O
the	O
occurrences	O
of	O
both	O
the	O
user	O
entered	O
words	O
and	O
synonyms	B-Application
and	O
alternate	O
morphological	O
forms	O
,	O
documents	O
with	O
a	O
higher	O
density	O
(	O
high	O
frequency	O
and	O
close	O
proximity	O
)	O
tend	O
to	O
migrate	O
higher	O
up	O
in	O
the	O
search	B-Application
results	I-Application
,	O
leading	O
to	O
a	O
higher	O
quality	O
of	O
the	O
search	B-Application
results	I-Application
near	O
the	O
top	O
of	O
the	O
results	O
,	O
despite	O
the	O
larger	O
recall	O
.	O
</s>
<s>
Automatic	O
methods	O
for	O
query	B-Algorithm
expansion	I-Algorithm
were	O
proposed	O
in	O
1960	O
by	O
Maron	O
and	O
Kuhns	O
.	O
</s>
<s>
Modern	O
query	B-Algorithm
expansion	I-Algorithm
methods	O
either	O
imply	O
document	O
collection	O
analysis	O
(	O
global	O
or	O
local	O
)	O
or	O
are	O
dictionary	O
-	O
or	O
ontology-based	O
.	O
</s>
<s>
The	O
local	O
analysis	O
refers	O
to	O
the	O
relevance	B-Application
feedback	I-Application
introduced	O
by	O
Rocchio	O
.	O
</s>
<s>
Rocchio	O
proposed	O
to	O
judge	O
manually	O
some	O
of	O
the	O
retrieved	O
documents	O
and	O
use	O
this	O
feedback	O
information	O
to	O
expand	O
the	O
query	B-Library
.	O
</s>
<s>
Pseudo-relevance	O
feedback	O
is	O
efficient	O
in	O
average	O
but	O
can	O
damage	O
results	O
for	O
some	O
queries	B-Library
,	O
especially	O
difficult	O
ones	O
since	O
the	O
top	O
retrieved	O
documents	O
are	O
probably	O
non-relevant	O
.	O
</s>
<s>
Pseudo-relevant	O
documents	O
are	O
used	O
to	O
find	O
expansion	O
candidate	O
terms	O
that	O
co-occur	O
with	O
many	O
query	B-Library
terms	O
.	O
</s>
<s>
This	O
idea	O
was	O
further	O
developed	O
within	O
the	O
relevance	O
language	B-Language
model	I-Language
formalism	O
in	O
positional	O
relevance	O
and	O
proximity	O
relevance	O
models	O
which	O
consider	O
the	O
distance	O
to	O
query	B-Library
terms	O
in	O
the	O
pseudo-relevant	O
documents	O
.	O
</s>
<s>
Another	O
direction	O
in	O
query	B-Algorithm
expansion	I-Algorithm
is	O
the	O
application	O
of	O
word	B-General_Concept
embeddings	I-General_Concept
.	O
</s>
<s>
An	O
alternative	O
to	O
query	B-Algorithm
expansion	I-Algorithm
is	O
document	O
expansion	O
,	O
which	O
reformulates	O
the	O
text	O
of	O
the	O
documents	O
being	O
searched	O
rather	O
than	O
the	O
text	O
of	O
the	O
query	B-Library
.	O
</s>
