<s>
Q-systems	B-General_Concept
are	O
a	O
method	O
of	O
directed	O
graph	O
transformations	O
according	O
to	O
given	O
grammar	O
rules	O
,	O
developed	O
at	O
the	O
Université	O
de	O
Montréal	O
by	O
Alain	O
Colmerauer	O
in	O
1967	O
–	O
70	O
for	O
use	O
in	O
natural	B-Language
language	I-Language
processing	I-Language
.	O
</s>
<s>
The	O
Université	O
de	O
Montréal	O
's	O
machine	B-Application
translation	I-Application
system	I-Application
,	O
TAUM-73	B-General_Concept
,	O
used	O
the	O
Q-Systems	B-General_Concept
as	O
its	O
language	O
formalism	O
.	O
</s>
<s>
The	O
data	O
structure	O
manipulated	O
by	O
a	O
Q-system	B-General_Concept
is	O
a	O
Q-graph	O
,	O
which	O
is	O
a	O
directed	O
acyclic	O
graph	O
with	O
one	O
entry	O
node	O
and	O
one	O
exit	O
node	O
,	O
where	O
each	O
arc	O
bears	O
a	O
labelled	O
ordered	O
tree	O
.	O
</s>
<s>
A	O
Q-System	B-General_Concept
consists	O
of	O
a	O
sequence	O
of	O
Q-treatments	O
,	O
each	O
being	O
a	O
set	O
of	O
Q-rules	O
,	O
of	O
the	O
form	O
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx1 ]	O
.	O
</s>
<s>
It	O
first	O
applies	O
all	O
its	O
rules	O
exhaustively	O
,	O
using	O
instantiation	O
(	O
one-way	O
unification	B-Algorithm
)	O
,	O
thereby	O
adding	O
new	O
paths	O
to	O
the	O
current	O
Q-graph	O
(	O
added	O
arcs	O
and	O
their	O
trees	O
can	O
be	O
used	O
to	O
produce	O
new	O
paths	O
)	O
.	O
</s>
<s>
That	O
allows	O
several	O
Q-Systems	B-General_Concept
to	O
be	O
chained	O
,	O
each	O
of	O
them	O
performing	O
a	O
specialized	O
task	O
,	O
together	O
forming	O
a	O
complex	O
system	O
.	O
</s>
<s>
For	O
example	O
,	O
TAUM	O
73	O
consisted	O
of	O
fifteen	O
chained	O
Q-Systems	B-General_Concept
.	O
</s>
<s>
An	O
extension	O
of	O
the	O
basic	O
idea	O
of	O
the	O
Q-Systems	B-General_Concept
,	O
namely	O
to	O
replace	O
instantiation	O
by	O
unification	B-Algorithm
(	O
to	O
put	O
it	O
simply	O
,	O
allow	O
"	O
new	O
"	O
variables	O
in	O
the	O
right	O
hand	O
side	O
part	O
of	O
a	O
rule	O
,	O
and	O
replace	O
parametrized	O
labelled	O
trees	O
by	O
logical	O
terms	O
)	O
led	O
to	O
Prolog	B-Language
,	O
designed	O
by	O
Alain	O
Colmerauer	O
and	O
Philippe	O
Roussel	O
in	O
1972	O
.	O
</s>
<s>
In	O
2009	O
,	O
Hong	O
Thai	O
Nguyen	O
of	O
GETALP	O
,	O
Laboratoire	O
d'Informatique	O
de	O
Grenoble	O
reimplemented	O
the	O
Q-language	O
in	O
C	O
,	O
using	O
ANTLR	O
to	O
compile	O
the	O
Q-systems	B-General_Concept
and	O
the	O
Q-graphs	O
,	O
and	O
an	O
algorithm	O
proposed	O
by	O
Christian	O
Boitet	O
(	O
as	O
none	O
had	O
been	O
published	O
and	O
sources	O
of	O
the	O
previous	O
Fortran	O
implementation	O
had	O
been	O
lost	O
)	O
.	O
</s>
