<s>
Query	B-General_Concept
understanding	I-General_Concept
is	O
the	O
process	O
of	O
inferring	O
the	O
intent	O
of	O
a	O
search	O
engine	O
user	O
by	O
extracting	O
semantic	O
meaning	O
from	O
the	O
searcher	O
’s	O
keywords	O
.	O
</s>
<s>
Query	B-General_Concept
understanding	I-General_Concept
methods	O
generally	O
take	O
place	O
before	O
the	O
search	O
engine	O
retrieves	B-Library
and	O
ranks	O
results	O
.	O
</s>
<s>
It	O
is	O
related	O
to	O
natural	B-Language
language	I-Language
processing	I-Language
but	O
specifically	O
focused	O
on	O
the	O
understanding	O
of	O
search	O
queries	B-Library
.	O
</s>
<s>
Query	B-General_Concept
understanding	I-General_Concept
is	O
at	O
the	O
heart	O
of	O
technologies	O
like	O
Amazon	B-Application
Alexa	I-Application
,	O
Apple	O
's	O
Siri	B-Application
.	O
</s>
<s>
Google	B-Application
Assistant	I-Application
,	O
IBM	O
's	O
Watson	B-Application
,	O
and	O
Microsoft	O
's	O
Cortana	B-Application
.	O
</s>
<s>
Spelling	B-Application
correction	I-Application
is	O
the	O
process	O
of	O
automatically	O
detecting	O
and	O
correcting	O
spelling	O
errors	O
in	O
search	O
queries	B-Library
.	O
</s>
<s>
Most	O
spelling	B-Application
correction	I-Application
algorithms	O
are	O
based	O
on	O
a	O
language	B-Language
model	I-Language
,	O
which	O
determines	O
the	O
a	O
priori	O
probability	O
of	O
an	O
intended	O
query	B-Library
,	O
and	O
an	O
error	O
model	O
(	O
typically	O
a	O
noisy	B-General_Concept
channel	I-General_Concept
model	I-General_Concept
)	O
,	O
which	O
determines	O
the	O
probability	O
of	O
a	O
particular	O
misspelling	O
,	O
given	O
an	O
intended	O
query	B-Library
.	O
</s>
<s>
The	O
languages	O
of	O
the	O
world	O
vary	O
in	O
how	O
much	O
morphological	O
variation	O
they	O
exhibit	O
,	O
and	O
for	O
some	O
languages	O
there	O
are	O
simple	O
methods	O
to	O
reduce	O
a	O
word	O
in	O
query	B-Library
to	O
its	O
lemma	O
or	O
root	O
form	O
or	O
its	O
stem	O
.	O
</s>
<s>
More	O
advanced	O
methods	O
,	O
lemmatisation	B-General_Concept
methods	O
,	O
group	O
together	O
the	O
inflected	O
forms	O
of	O
a	O
word	O
through	O
more	O
complex	O
rule	O
sets	O
based	O
on	O
a	O
word	O
’s	O
part	O
of	O
speech	O
or	O
its	O
record	O
in	O
a	O
lexical	O
database	O
,	O
transforming	O
an	O
inflected	O
word	O
through	O
lookup	O
or	O
a	O
series	O
of	O
transformations	O
to	O
its	O
lemma	O
.	O
</s>
<s>
Once	O
the	O
attention	O
of	O
the	O
information	B-Library
retrieval	I-Library
field	O
moved	O
to	O
languages	O
other	O
than	O
English	O
,	O
it	O
was	O
found	O
that	O
for	O
some	O
languages	O
there	O
were	O
obvious	O
gains	O
to	O
be	O
found	O
.	O
</s>
<s>
Named-entity	B-General_Concept
recognition	I-General_Concept
specifically	O
focuses	O
on	O
named	B-General_Concept
entities	I-General_Concept
,	O
such	O
as	O
names	O
of	O
people	O
,	O
places	O
,	O
and	O
organizations	O
.	O
</s>
<s>
In	O
addition	O
,	O
entity	O
recognition	O
includes	O
identifying	O
concepts	O
in	O
queries	B-Library
that	O
may	O
be	O
represented	O
by	O
multi-word	O
phrases	O
.	O
</s>
<s>
Query	B-Library
rewriting	O
is	O
the	O
process	O
of	O
automatically	O
reformulating	O
a	O
search	O
query	B-Library
to	O
more	O
accurately	O
capture	O
its	O
intent	O
.	O
</s>
<s>
Query	B-Algorithm
expansion	I-Algorithm
adds	O
additional	O
query	B-Library
terms	O
,	O
such	O
as	O
synonyms	O
,	O
in	O
order	O
to	O
retrieve	O
more	O
documents	O
and	O
thereby	O
increase	O
recall	O
.	O
</s>
<s>
Query	B-Library
relaxation	O
removes	O
query	B-Library
terms	O
to	O
reduce	O
the	O
requirements	O
for	O
a	O
document	O
to	O
match	O
the	O
query	B-Library
,	O
thereby	O
also	O
increasing	O
recall	O
.	O
</s>
<s>
Other	O
forms	O
of	O
query	B-Library
rewriting	O
,	O
such	O
as	O
automatically	O
converting	O
consecutive	O
query	B-Library
terms	O
into	O
phrases	O
and	O
restricting	O
query	B-Library
terms	O
to	O
specific	O
fields	B-Application
,	O
aim	O
to	O
increase	O
precision	O
.	O
</s>
<s>
Apache	O
Lucene	O
search	O
engine	O
uses	O
query	B-Library
rewrite	O
to	O
transform	O
complex	O
queries	B-Library
to	O
more	O
primitive	O
queries	B-Library
,	O
such	O
as	O
expressions	O
with	O
wildcards	O
(	O
e.g.	O
</s>
<s>
quer*	O
)	O
into	O
a	O
boolean	O
query	B-Library
of	O
the	O
matching	O
terms	O
from	O
the	O
index	O
(	O
such	O
as	O
query	B-Library
OR	O
queries	B-Library
)	O
.	O
</s>
