<s>
The	O
Object	B-Language
Constraint	I-Language
Language	I-Language
(	O
OCL	O
)	O
is	O
a	O
declarative	B-Language
language	I-Language
describing	O
rules	O
applying	O
to	O
Unified	B-Language
Modeling	I-Language
Language	I-Language
(	O
UML	B-Language
)	O
models	O
developed	O
at	O
IBM	O
and	O
is	O
now	O
part	O
of	O
the	O
UML	B-Language
standard	O
.	O
</s>
<s>
Initially	O
,	O
OCL	O
was	O
merely	O
a	O
formal	O
specification	O
language	O
extension	O
for	O
UML	B-Language
.	O
</s>
<s>
OCL	O
may	O
now	O
be	O
used	O
with	O
any	O
Meta-Object	B-Application
Facility	I-Application
(	O
MOF	B-Application
)	O
Object	B-Architecture
Management	I-Architecture
Group	I-Architecture
(	O
OMG	B-Architecture
)	O
meta-model	O
,	O
including	O
UML	B-Language
.	O
</s>
<s>
The	O
Object	B-Language
Constraint	I-Language
Language	I-Language
is	O
a	O
precise	O
text	O
language	O
that	O
provides	O
constraint	O
and	O
object	O
query	O
expressions	O
on	O
any	O
MOF	B-Application
model	O
or	O
meta-model	O
that	O
cannot	O
otherwise	O
be	O
expressed	O
by	O
diagrammatic	O
notation	O
.	O
</s>
<s>
OCL	O
is	O
a	O
key	O
component	O
of	O
the	O
new	O
OMG	B-Architecture
standard	O
recommendation	O
for	O
transforming	O
models	O
,	O
the	O
Queries/Views/Transformations	O
(	O
QVT	B-Language
)	O
specification	O
.	O
</s>
<s>
OCL	O
is	O
a	O
descendant	O
of	O
Syntropy	B-Application
,	O
a	O
second-generation	O
object-oriented	B-Application
analysis	I-Application
and	I-Application
design	I-Application
method	O
.	O
</s>
<s>
OCL	O
supplements	O
UML	B-Language
by	O
providing	O
expressions	O
that	O
have	O
neither	O
the	O
ambiguities	O
of	O
natural	O
language	O
nor	O
the	O
inherent	O
difficulty	O
of	O
using	O
complex	O
mathematics	O
.	O
</s>
<s>
OCL	O
makes	O
a	O
Meta-Object	B-Application
Facility	I-Application
model	O
more	O
precise	O
by	O
associating	O
assertions	O
with	O
its	O
meta-elements	O
.	O
</s>
<s>
Of	O
particular	O
importance	O
to	O
Model	B-Language
Driven	I-Language
Engineering	I-Language
(	O
MDE	O
)	O
or	O
model-driven	B-Architecture
architecture	I-Architecture
is	O
the	O
notion	O
of	O
Model	B-Language
transformation	I-Language
.	O
</s>
<s>
The	O
OMG	B-Architecture
has	O
defined	O
a	O
specific	O
standard	O
for	O
model	B-Language
transformation	I-Language
called	O
MOF/QVT	O
or	O
in	O
short	O
QVT	B-Language
.	O
</s>
<s>
Several	O
model	B-Language
transformation	I-Language
languages	I-Language
like	O
GReAT	O
,	O
VIATRA	B-Application
,	O
or	O
Tefkat	B-Language
are	O
presently	O
available	O
,	O
with	O
different	O
levels	O
of	O
compliance	O
with	O
the	O
QVT	B-Language
standard	O
.	O
</s>
<s>
Many	O
of	O
these	O
languages	O
are	O
built	O
on	O
top	O
of	O
OCL	O
,	O
which	O
is	O
the	O
main	O
part	O
of	O
the	O
QVT-compliance	O
.	O
</s>
<s>
Being	O
a	O
rule-based	O
validation	O
language	O
,	O
Schematron	B-Language
may	O
be	O
considered	O
an	O
alternative	O
to	O
OCL	O
.	O
</s>
<s>
However	O
Schematron	B-Language
works	O
for	O
Extensible	B-Protocol
Markup	I-Protocol
Language	I-Protocol
(	O
XML	B-Protocol
)	O
trees	O
while	O
OCL	O
makes	O
it	O
possible	O
to	O
navigate	O
MOF-based	O
models	O
and	O
meta-models	O
(	O
i.e.	O
</s>
<s>
XML	B-Language
Metadata	I-Language
Interchange	I-Language
(	O
XMI	B-Language
)	O
trees	O
)	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
OCL	O
relates	O
to	O
UML	B-Language
or	O
MOF	B-Application
similarly	O
to	O
how	O
Schematron	B-Language
relates	O
to	O
XML	B-Protocol
.	O
</s>
<s>
(	O
Note	O
that	O
Schematron	B-Language
uses	O
XPath	B-Language
to	O
navigate	O
inside	O
the	O
XML	B-Language
trees	I-Language
.	O
</s>
<s>
)	O
Being	O
a	O
model	O
specification	O
language	O
permitting	O
designers	O
to	O
decorate	O
a	O
model	O
or	O
a	O
meta-model	O
with	O
side-effect-free	O
annotations	O
,	O
OCL	O
could	O
be	O
replaced	O
by	O
languages	O
like	O
Alloy	B-Application
.	O
</s>
<s>
Eclipse	B-Application
OCL	O
extends	O
Standard	O
OCL	O
with	O
additional	O
operators	O
and	O
a	O
type	O
for	O
Maps	O
.	O
</s>
