<s>
Wrapper	B-Algorithm
in	O
data	B-Application
mining	I-Application
is	O
a	O
procedure	O
that	O
extracts	O
regular	O
subcontent	O
of	O
an	O
unstructured	O
or	O
loosely-structured	O
information	O
source	O
and	O
translates	O
it	O
into	O
a	O
relational	B-Architecture
form	I-Architecture
,	O
so	O
it	O
can	O
be	O
processed	O
as	O
structured	O
data	O
.	O
</s>
<s>
Wrapper	B-Algorithm
induction	O
is	O
the	O
problem	O
of	O
devising	O
extraction	O
procedures	O
on	O
an	O
automatic	O
basis	O
,	O
with	O
minimal	O
reliance	O
on	O
hand-crafted	O
rules	O
.	O
</s>
<s>
–	O
wrapped	O
in	O
a	O
loosely	O
structured	O
presentation	O
language	O
(	O
usually	O
some	O
variant	O
of	O
HTML	B-Language
)	O
,	O
formatted	O
for	O
human	O
browsing	O
and	O
navigation	O
.	O
</s>
<s>
Software	O
systems	O
using	O
such	O
resources	O
must	O
translate	O
HTML	B-Language
content	O
into	O
a	O
relational	B-Architecture
form	I-Architecture
.	O
</s>
<s>
Wrappers	B-Algorithm
are	O
commonly	O
used	O
as	O
such	O
translators	O
.	O
</s>
<s>
Formally	O
,	O
a	O
wrapper	B-Algorithm
is	O
a	O
function	O
from	O
a	O
page	O
to	O
the	O
set	O
of	O
tuples	B-Application
it	O
contains	O
.	O
</s>
<s>
There	O
are	O
two	O
main	O
approaches	O
to	O
wrapper	B-Algorithm
generation	O
:	O
wrapper	B-Algorithm
induction	O
and	O
automated	O
data	B-General_Concept
extraction	I-General_Concept
.	O
</s>
<s>
Wrapper	B-Algorithm
induction	O
uses	O
supervised	O
learning	O
to	O
learn	O
data	B-General_Concept
extraction	I-General_Concept
rules	O
from	O
manually	O
labeled	O
training	O
examples	O
.	O
</s>
<s>
the	O
difficulty	O
of	O
wrapper	B-Algorithm
maintenance	O
.	O
</s>
<s>
Due	O
to	O
the	O
manual	O
labeling	O
effort	O
,	O
it	O
is	O
hard	O
to	O
extract	O
data	O
from	O
a	O
large	O
number	O
of	O
sites	O
as	O
each	O
site	O
has	O
its	O
own	O
templates	O
and	O
requires	O
separate	O
manual	O
labeling	O
for	O
wrapper	B-Algorithm
learning	O
.	O
</s>
<s>
Wrapper	B-Algorithm
maintenance	O
is	O
also	O
a	O
major	O
issue	O
because	O
whenever	O
a	O
site	O
changes	O
the	O
wrappers	B-Algorithm
built	O
for	O
the	O
site	O
become	O
obsolete	O
.	O
</s>
<s>
Due	O
to	O
these	O
shortcomings	O
,	O
researchers	O
have	O
studied	O
automated	O
wrapper	B-Algorithm
generation	O
using	O
unsupervised	O
pattern	O
mining	O
.	O
</s>
<s>
Wrapper	B-Algorithm
generation	O
on	O
the	O
Web	O
is	O
an	O
important	O
problem	O
with	O
a	O
wide	O
range	O
of	O
applications	O
.	O
</s>
