<s>
Lemmatisation	B-General_Concept
(	O
or	O
lemmatization	B-General_Concept
)	O
in	O
linguistics	O
is	O
the	O
process	O
of	O
grouping	O
together	O
the	O
inflected	O
forms	O
of	O
a	O
word	O
so	O
they	O
can	O
be	O
analysed	O
as	O
a	O
single	O
item	O
,	O
identified	O
by	O
the	O
word	O
's	O
lemma	O
,	O
or	O
dictionary	O
form	O
.	O
</s>
<s>
In	O
computational	O
linguistics	O
,	O
lemmatisation	B-General_Concept
is	O
the	O
algorithmic	O
process	O
of	O
determining	O
the	O
lemma	O
of	O
a	O
word	O
based	O
on	O
its	O
intended	O
meaning	O
.	O
</s>
<s>
Unlike	O
stemming	B-General_Concept
,	O
lemmatisation	B-General_Concept
depends	O
on	O
correctly	O
identifying	O
the	O
intended	O
part	O
of	O
speech	O
and	O
meaning	O
of	O
a	O
word	O
in	O
a	O
sentence	O
,	O
as	O
well	O
as	O
within	O
the	O
larger	O
context	O
surrounding	O
that	O
sentence	O
,	O
such	O
as	O
neighboring	O
sentences	O
or	O
even	O
an	O
entire	O
document	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
developing	O
efficient	O
lemmatisation	B-General_Concept
algorithms	O
is	O
an	O
open	O
area	O
of	O
research	O
.	O
</s>
<s>
Lemmatisation	B-General_Concept
is	O
closely	O
related	O
to	O
stemming	B-General_Concept
.	O
</s>
<s>
In	O
fact	O
,	O
when	O
used	O
within	O
information	O
retrieval	O
systems	O
,	O
stemming	B-General_Concept
improves	O
query	O
recall	O
accuracy	O
,	O
or	O
true	O
positive	O
rate	O
,	O
when	O
compared	O
to	O
lemmatisation	B-General_Concept
.	O
</s>
<s>
Nonetheless	O
,	O
stemming	B-General_Concept
reduces	O
precision	O
,	O
or	O
the	O
proportion	O
of	O
positively-labeled	O
instances	O
that	O
are	O
actually	O
positive	O
,	O
for	O
such	O
systems	O
.	O
</s>
<s>
This	O
link	O
is	O
missed	O
by	O
stemming	B-General_Concept
,	O
as	O
it	O
requires	O
a	O
dictionary	O
look-up	O
.	O
</s>
<s>
The	O
word	O
"	O
walk	O
"	O
is	O
the	O
base	O
form	O
for	O
the	O
word	O
"	O
walking	O
"	O
,	O
and	O
hence	O
this	O
is	O
matched	O
in	O
both	O
stemming	B-General_Concept
and	O
lemmatisation	B-General_Concept
.	O
</s>
<s>
Unlike	O
stemming	B-General_Concept
,	O
lemmatisation	B-General_Concept
attempts	O
to	O
select	O
the	O
correct	O
lemma	O
depending	O
on	O
the	O
context	O
.	O
</s>
<s>
Document	O
indexing	O
software	O
like	O
Lucene	B-Language
can	O
store	O
the	O
base	O
stemmed	O
format	O
of	O
the	O
word	O
without	O
the	O
knowledge	O
of	O
meaning	O
,	O
but	O
only	O
considering	O
word	O
formation	O
grammar	O
rules	O
.	O
</s>
<s>
This	O
is	O
because	O
the	O
purpose	O
of	O
stemming	B-General_Concept
is	O
not	O
to	O
produce	O
the	O
appropriate	O
lemma	O
–	O
that	O
is	O
a	O
more	O
challenging	O
task	O
that	O
requires	O
knowledge	O
of	O
context	O
.	O
</s>
<s>
The	O
main	O
purpose	O
of	O
stemming	B-General_Concept
is	O
to	O
map	O
different	O
forms	O
of	O
a	O
word	O
to	O
a	O
single	O
form	O
.	O
</s>
<s>
A	O
trivial	O
way	O
to	O
do	O
lemmatization	B-General_Concept
is	O
by	O
simple	O
dictionary	O
lookup	O
.	O
</s>
<s>
Morphological	O
processing	O
of	O
biomedical	O
text	O
can	O
be	O
more	O
effective	O
by	O
a	O
specialised	O
lemmatisation	B-General_Concept
program	O
for	O
biomedicine	O
,	O
and	O
may	O
improve	O
the	O
accuracy	O
of	O
practical	O
information	B-General_Concept
extraction	I-General_Concept
tasks	O
.	O
</s>
