<s>
In	O
artificial	B-Application
intelligence	I-Application
,	O
preference-based	B-Application
planning	I-Application
is	O
a	O
form	O
of	O
automated	B-Application
planning	I-Application
and	I-Application
scheduling	I-Application
which	O
focuses	O
on	O
producing	O
plans	O
that	O
additionally	O
satisfy	O
as	O
many	O
user-specified	O
preferences	O
as	O
possible	O
.	O
</s>
<s>
Examples	O
of	O
preference-based	B-Application
planning	I-Application
software	O
include	O
PPLAN	O
and	O
HTNPlan-P	O
(	O
preference-based	O
HTN	B-Application
planning	I-Application
)	O
.	O
</s>
<s>
This	O
differs	O
from	O
hard	O
constraints	O
which	O
must	O
be	O
satisfied	O
in	O
all	O
plans	O
produced	O
by	O
the	O
planning	B-Application
software	I-Application
.	O
</s>
<s>
The	O
planning	B-Application
software	I-Application
could	O
now	O
plan	O
to	O
visit	O
Starbucks	B-Application
first	O
and	O
then	O
continue	O
to	O
school	O
.	O
</s>
<s>
The	O
Planning	B-Application
Domain	I-Application
Definition	I-Application
Language	I-Application
(	O
as	O
of	O
version	O
3.0	O
)	O
supports	O
the	O
specification	O
of	O
preferences	O
through	O
preference	O
statements	O
.	O
</s>
<s>
As	O
this	O
example	O
shows	O
,	O
a	O
preference	O
is	O
evaluated	O
with	O
regard	O
to	O
all	O
states	O
of	O
a	O
plan	O
(	O
if	O
semantically	B-Application
required	O
)	O
.	O
</s>
<s>
For	O
this	O
purpose	O
,	O
PDDL	B-Application
3.0	O
includes	O
an	O
expression	O
called	O
is-violated	O
<name>	O
which	O
is	O
equal	O
to	O
"	O
the	O
number	O
of	O
distinct	O
preferences	O
with	O
the	O
given	O
name	O
that	O
are	O
not	O
satisfied	O
in	O
the	O
plan	O
"	O
.	O
</s>
<s>
In	O
the	O
area	O
of	O
constraint	B-Application
satisfaction	I-Application
problems	I-Application
,	O
flexible	O
variants	O
exist	O
that	O
deal	O
with	O
soft	O
constraints	O
in	O
a	O
similar	O
way	O
to	O
preferences	O
in	O
preference-based	B-Application
planning	I-Application
.	O
</s>
