<s>
An	O
algebraic	B-Language
Petri	I-Language
net	I-Language
(	O
APN	O
)	O
is	O
an	O
evolution	O
of	O
the	O
well	O
known	O
Petri	B-Operating_System
net	I-Operating_System
in	O
which	O
elements	O
of	O
user	O
defined	O
data	O
types	O
(	O
called	O
algebraic	O
abstract	O
data	O
types	O
(	O
AADT	O
)	O
)	O
replace	O
black	O
tokens	O
.	O
</s>
<s>
This	O
formalism	O
can	O
be	O
compared	O
to	O
coloured	O
Petri	B-Operating_System
nets	I-Operating_System
(	O
CPN	O
)	O
in	O
many	O
aspects	O
.	O
</s>
<s>
Algebraic	B-Language
Petri	I-Language
nets	I-Language
were	O
invented	O
by	O
Jacques	O
Vautherin	O
in	O
1985	O
in	O
his	O
PhD	O
thesis	O
and	O
later	O
improved	O
by	O
Wolfang	O
Reisig	O
.	O
</s>
<s>
The	O
control	O
part	O
which	O
is	O
handled	O
by	O
a	O
Petri	B-Operating_System
net	I-Operating_System
.	O
</s>
<s>
The	O
following	O
picture	O
describes	O
an	O
algebraic	B-Language
Petri	I-Language
net	I-Language
model	O
of	O
the	O
"	O
dining	O
philosophers	O
problem	O
"	O
.	O
</s>
<s>
Places	O
contain	O
multiset	B-Language
(	O
bags	O
)	O
of	O
tokens	O
.	O
</s>
<s>
Each	O
place	O
contains	O
one	O
and	O
only	O
one	O
multiset	B-Language
of	O
terms	O
,	O
the	O
place	O
is	O
typed	O
by	O
its	O
multiset	B-Language
.	O
</s>
<s>
Arcs	O
can	O
be	O
labeled	O
with	O
multisets	B-Language
of	O
either	O
closed	O
or	O
free	O
terms	O
.	O
</s>
<s>
Algebraic	B-Language
Petri	I-Language
nets	I-Language
are	O
the	O
basic	O
formalism	O
of	O
more	O
advanced	O
ones	O
such	O
as	O
CO-OPN	B-Language
.	O
</s>
