<s>
YAWL	B-Language
(	O
Yet	O
Another	O
Workflow	B-Operating_System
Language	O
)	O
is	O
a	O
workflow	B-Operating_System
language	O
based	O
on	O
workflow	B-Operating_System
patterns	O
.	O
</s>
<s>
It	O
is	O
available	O
as	O
open-source	B-Application
software	I-Application
under	O
the	O
LGPL	B-Application
license	I-Application
.	O
</s>
<s>
Production-level	O
implementations	O
of	O
YAWL	B-Language
include	O
deployment	O
by	O
first:utility	O
and	O
first:telecom	O
in	O
the	O
UK	O
to	O
automate	O
frontend	O
service	O
processes	O
,	O
and	O
by	O
the	O
Australian	O
film	O
television	O
and	O
radio	O
school	O
to	O
coordinate	O
film	O
shooting	O
processes	O
.	O
</s>
<s>
Comprehensive	O
support	O
for	O
the	O
workflow	B-Operating_System
patterns	O
.	O
</s>
<s>
Support	O
for	O
advanced	O
resource	B-Algorithm
allocation	I-Algorithm
policies	O
,	O
including	O
four-eyes	O
principle	O
and	O
chained	O
execution	O
.	O
</s>
<s>
Support	O
for	O
dynamic	O
adaptation	O
of	O
workflow	B-Operating_System
models	O
through	O
the	O
notion	O
of	O
worklets	O
.	O
</s>
<s>
Sophisticated	O
workflow	B-Operating_System
model	O
validation	O
features	O
(	O
e.g.	O
</s>
<s>
deadlock	B-Operating_System
detection	O
at	O
design-time	O
)	O
.	O
</s>
<s>
XML-based	O
model	O
for	O
data	O
definition	O
and	O
manipulation	O
based	O
on	O
XML	O
Schema	O
,	O
XPath	B-Language
and	O
XQuery	B-Language
.	O
</s>
<s>
XML-based	O
interfaces	O
for	O
monitoring	O
and	O
controlling	O
workflow	B-Operating_System
instances	O
and	O
for	O
accessing	O
execution	O
logs	O
.	O
</s>
<s>
The	O
original	O
drivers	O
behind	O
YAWL	B-Language
were	O
to	O
define	O
a	O
workflow	B-Operating_System
language	O
that	O
would	O
support	O
all	O
(	O
or	O
most	O
)	O
of	O
the	O
workflow	B-Operating_System
patterns	O
and	O
that	O
would	O
have	O
a	O
formal	O
semantics	O
.	O
</s>
<s>
Observing	O
that	O
Petri	B-Operating_System
nets	I-Operating_System
came	O
close	O
to	O
supporting	O
most	O
of	O
the	O
workflow	B-Operating_System
patterns	O
,	O
the	O
designers	O
of	O
YAWL	B-Language
decided	O
to	O
take	O
Petri	B-Operating_System
nets	I-Operating_System
as	O
a	O
starting	O
point	O
and	O
to	O
extend	O
this	O
formalism	O
with	O
three	O
main	O
constructs	O
,	O
namely	O
or-join	O
,	O
cancellation	O
sets	O
,	O
and	O
multi-instance	O
activities	O
.	O
</s>
<s>
These	O
three	O
concepts	O
are	O
aimed	O
at	O
supporting	O
five	O
of	O
the	O
workflow	B-Operating_System
patterns	O
that	O
were	O
not	O
directly	O
supported	O
in	O
Petri	B-Operating_System
nets	I-Operating_System
,	O
namely	O
synchronizing	O
merge	O
,	O
discriminator	O
,	O
N-out-of-M	O
join	O
,	O
multiple	O
instance	O
with	O
no	O
a	O
priori	O
runtime	O
knowledge	O
and	O
cancel	O
case	O
.	O
</s>
<s>
In	O
addition	O
,	O
YAWL	B-Language
adds	O
some	O
syntactical	O
elements	O
to	O
Petri	B-Operating_System
nets	I-Operating_System
in	O
order	O
to	O
intuitively	O
capture	O
other	O
workflow	B-Operating_System
patterns	O
such	O
as	O
simple	O
choice	O
(	O
xor-split	O
)	O
,	O
simple	O
merge	O
(	O
xor-join	O
)	O
,	O
and	O
multiple	O
choice	O
(	O
or-split	O
)	O
.	O
</s>
<s>
During	O
the	O
design	O
of	O
the	O
language	O
,	O
it	O
turned	O
out	O
that	O
some	O
of	O
the	O
extensions	O
that	O
were	O
added	O
to	O
Petri	B-Operating_System
nets	I-Operating_System
were	O
difficult	O
or	O
even	O
impossible	O
to	O
re-encode	O
back	O
into	O
plain	O
Petri	B-Operating_System
nets	I-Operating_System
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
original	O
formal	O
semantics	O
of	O
YAWL	B-Language
are	O
defined	O
as	O
a	O
labelled	B-Application
transition	I-Application
system	I-Application
and	O
not	O
in	O
terms	O
of	O
Petri	B-Operating_System
nets	I-Operating_System
.	O
</s>
<s>
The	O
fact	O
that	O
YAWL	B-Language
is	O
based	O
on	O
formal	O
semantics	O
has	O
enabled	O
the	O
implementation	O
of	O
several	O
techniques	O
for	O
analyzing	O
YAWL	B-Language
processes	O
.	O
</s>
<s>
In	O
particular	O
,	O
the	O
YAWL	B-Language
system	O
includes	O
a	O
static	O
analysis	O
tool	O
called	O
WofYAWL	O
.	O
</s>
<s>
YAWL	B-Language
is	O
sometimes	O
seen	O
as	O
an	O
alternative	O
to	O
BPEL	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
BPEL	O
is	O
supported	O
by	O
a	O
significant	O
number	O
of	O
tools	O
(	O
both	O
proprietary	O
and	O
open-source	B-Application
)	O
while	O
YAWL	B-Language
has	O
a	O
single	O
implementation	O
at	O
present	O
.	O
</s>
<s>
Also	O
,	O
several	O
researchers	O
have	O
captured	O
the	O
formal	O
semantics	O
of	O
subsets	O
of	O
BPEL	O
in	O
terms	O
of	O
various	O
formalisms	O
,	O
including	O
Petri	B-Operating_System
nets	I-Operating_System
,	O
process	O
algebra	O
and	O
finite	B-Architecture
state	I-Architecture
machine	I-Architecture
.	O
</s>
<s>
This	O
has	O
paved	O
the	O
way	O
for	O
the	O
development	O
of	O
static	O
analysis	O
tools	O
for	O
BPEL	O
that	O
can	O
compete	O
with	O
the	O
static	O
analysis	O
capabilities	O
provided	O
by	O
the	O
YAWL	B-Language
system	O
.	O
</s>
<s>
In	O
contrast	O
,	O
YAWL	B-Language
provides	O
a	O
unified	O
interface	O
for	O
worklist	O
services	O
based	O
on	O
web	O
services	O
standards	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
YAWL	B-Language
system	O
comes	O
with	O
a	O
default	O
worklist	O
service	O
that	O
supports	O
several	O
types	O
of	O
human	O
task	O
allocation	O
and	O
handling	O
.	O
</s>
<s>
Another	O
advantage	O
of	O
YAWL	B-Language
is	O
its	O
support	O
for	O
workflow	B-Operating_System
patterns	O
,	O
although	O
the	O
gap	O
between	O
YAWL	B-Language
and	O
BPEL	O
in	O
this	O
respect	O
may	O
be	O
reduced	O
by	O
new	O
constructs	O
that	O
are	O
included	O
in	O
BPEL	O
version	O
2.0	O
.	O
</s>
