<s>
In	O
linguistics	O
,	O
aggregation	B-General_Concept
is	O
a	O
subtask	O
of	O
natural	B-General_Concept
language	I-General_Concept
generation	I-General_Concept
,	O
which	O
involves	O
merging	O
syntactic	O
constituents	O
(	O
such	O
as	O
sentences	O
and	O
phrases	O
)	O
together	O
.	O
</s>
<s>
Sometimes	O
aggregation	B-General_Concept
can	O
be	O
done	O
at	O
a	O
conceptual	O
level	O
.	O
</s>
<s>
A	O
simple	O
example	O
of	O
syntactic	O
aggregation	B-General_Concept
is	O
merging	O
the	O
two	O
sentences	O
John	O
went	O
to	O
the	O
shop	O
and	O
John	O
bought	O
an	O
apple	O
into	O
the	O
single	O
sentence	O
John	O
went	O
to	O
the	O
shop	O
and	O
bought	O
an	O
apple	O
.	O
</s>
<s>
Syntactic	O
aggregation	B-General_Concept
can	O
be	O
much	O
more	O
complex	O
than	O
this	O
.	O
</s>
<s>
For	O
example	O
,	O
aggregation	B-General_Concept
can	O
embed	O
one	O
of	O
the	O
constituents	O
in	O
the	O
other	O
;	O
e.g.	O
,	O
we	O
can	O
aggregate	O
John	O
went	O
to	O
the	O
shop	O
and	O
The	O
shop	O
was	O
closed	O
into	O
the	O
sentence	O
John	O
went	O
to	O
the	O
shop	O
,	O
which	O
was	O
closed	O
.	O
</s>
<s>
Aggregation	B-General_Concept
algorithms	O
must	O
do	O
two	O
things	O
:	O
</s>
<s>
Aggegration	O
decisions	O
certainly	O
depend	O
on	O
the	O
semantic	B-Application
relations	O
between	O
the	O
constituents	O
,	O
as	O
mentioned	O
above	O
;	O
they	O
also	O
depend	O
on	O
the	O
genre	O
(	O
e.g.	O
,	O
bureaucratic	O
texts	O
tend	O
to	O
be	O
more	O
aggregated	O
than	O
instruction	O
manuals	O
)	O
.	O
</s>
<s>
With	O
regard	O
to	O
the	O
second	O
issue	O
,	O
there	O
have	O
been	O
some	O
studies	O
of	O
different	O
types	O
of	O
aggregation	B-General_Concept
,	O
and	O
how	O
they	O
should	O
be	O
carried	O
out	O
.	O
</s>
<s>
Harbusch	O
and	O
Kempen	O
describe	O
several	O
syntactic	O
aggregation	B-General_Concept
strategies	O
.	O
</s>
<s>
Much	O
less	O
is	O
known	O
about	O
conceptual	O
aggregation	B-General_Concept
.	O
</s>
<s>
show	O
how	O
conceptual	O
aggregation	B-General_Concept
can	O
be	O
done	O
in	O
an	O
intelligent	O
tutoring	O
system	O
,	O
and	O
demonstrate	O
that	O
performing	O
such	O
aggregation	B-General_Concept
makes	O
the	O
system	O
more	O
effective	O
(	O
and	O
that	O
conceptual	O
aggregation	B-General_Concept
make	O
a	O
bigger	O
impact	O
than	O
syntactic	O
aggregation	B-General_Concept
)	O
.	O
</s>
<s>
Unfortunately	O
there	O
is	O
not	O
much	O
software	O
available	O
for	O
performing	O
aggregation	B-General_Concept
.	O
</s>
<s>
However	O
the	O
SimpleNLG	O
system	O
does	O
include	O
limited	O
support	O
for	O
basic	O
aggregation	B-General_Concept
.	O
</s>
