<s>
Executable	B-Language
UML	I-Language
(	O
xtUML	B-Language
or	O
xUML	B-Language
)	O
is	O
both	O
a	O
software	O
development	O
method	O
and	O
a	O
highly	O
abstract	B-Application
software	O
language	O
.	O
</s>
<s>
It	O
was	O
described	O
for	O
the	O
first	O
time	O
in	O
2002	O
in	O
the	O
book	O
"	O
Executable	B-Language
UML	I-Language
:	O
A	O
Foundation	O
for	O
Model-Driven	B-Architecture
Architecture	I-Architecture
"	O
.	O
</s>
<s>
The	O
language	O
"	O
combines	O
a	O
subset	O
of	O
the	O
UML	B-Language
(	O
Unified	B-Language
Modeling	I-Language
Language	I-Language
)	O
graphical	O
notation	O
with	O
executable	O
semantics	O
and	O
timing	O
rules.	O
"	O
</s>
<s>
The	O
Executable	B-Language
UML	I-Language
method	O
is	O
the	O
successor	O
to	O
the	O
Shlaer	O
–	O
Mellor	O
method	O
.	O
</s>
<s>
Executable	B-Language
UML	I-Language
models	O
"	O
can	O
be	O
run	O
,	O
tested	O
,	O
debugged	O
,	O
and	O
measured	O
for	O
performance	O
.	O
</s>
<s>
"	O
,	O
and	O
can	O
be	O
compiled	B-Language
into	O
a	O
less	O
abstract	B-Application
programming	O
language	O
to	O
target	O
a	O
specific	O
implementation	O
.	O
</s>
<s>
Executable	B-Language
UML	I-Language
supports	O
model-driven	B-Architecture
architecture	I-Architecture
(	O
MDA	B-Architecture
)	O
through	O
specification	O
of	O
platform-independent	B-Architecture
models	I-Architecture
,	O
and	O
the	O
compilation	B-Language
of	O
the	O
platform-independent	B-Architecture
models	I-Architecture
into	O
platform-specific	B-Architecture
models	I-Architecture
.	O
</s>
<s>
Executable	B-Language
UML	I-Language
is	O
a	O
higher	O
level	O
of	O
abstraction	B-Application
than	O
third-generation	O
programming	O
languages	O
.	O
</s>
<s>
This	O
allows	O
developers	B-Application
to	O
develop	O
at	O
the	O
level	O
of	O
abstraction	B-Application
of	O
the	O
application	O
.	O
</s>
<s>
The	O
Executable	B-Language
UML	I-Language
aims	O
for	O
separation	O
of	O
concerns	O
.	O
</s>
<s>
This	O
also	O
enables	O
Executable	B-Language
UML	I-Language
domains	O
to	O
be	O
cross-platform	B-Operating_System
.	O
</s>
<s>
Executable	B-Language
UML	I-Language
also	O
allows	O
for	O
translation	O
of	O
platform-independent	B-Architecture
models	I-Architecture
(	O
PIM	B-Architecture
)	O
into	O
platform-specific	B-Architecture
models	I-Architecture
(	O
PSM	B-Architecture
)	O
.	O
</s>
<s>
The	O
Executable	B-Language
UML	I-Language
method	O
enables	O
valuing	O
the	O
model	O
as	O
intellectual	O
property	O
,	O
since	O
the	O
model	O
is	O
a	O
fully	O
executable	O
solution	O
for	O
the	O
problem	O
space	O
.	O
</s>
<s>
Actions	O
are	O
specified	O
in	O
action	B-Language
language	I-Language
.	O
</s>
<s>
This	O
means	O
that	O
the	O
automatic	O
generation	O
of	O
implementation	O
code	O
from	O
Executable	B-Language
UML	I-Language
models	O
can	O
be	O
output	O
in	O
an	O
optimized	O
form	O
.	O
</s>
<s>
Executable	B-Language
UML	I-Language
is	O
intended	O
to	O
serve	O
as	O
executable	O
code	O
as	O
well	O
as	O
documentation	O
.	O
</s>
<s>
The	O
models	O
are	O
a	O
graphical	O
,	O
executable	O
specification	O
of	O
the	O
problem	O
space	O
that	O
is	O
compiled	B-Language
into	O
a	O
target	O
implementation	O
.	O
</s>
<s>
They	O
are	O
also	O
intended	O
to	O
be	O
human-readable	B-General_Concept
.	O
</s>
<s>
A	O
system	B-Application
is	O
composed	O
of	O
multiple	O
subject	O
matters	O
,	O
known	O
as	O
domains	O
in	O
Executable	B-Language
UML	I-Language
terms	O
.	O
</s>
<s>
Executable	B-Language
UML	I-Language
is	O
used	O
to	O
model	O
a	O
domain	B-Application
at	O
the	O
level	O
of	O
abstraction	B-Application
of	O
its	O
subject	O
matter	O
independent	O
of	O
implementation	O
concerns	O
.	O
</s>
<s>
The	O
resulting	O
domain	B-Application
model	O
is	O
represented	O
by	O
the	O
following	O
elements	O
:	O
</s>
<s>
The	O
domain	B-Application
chart	O
provides	O
a	O
view	O
of	O
the	O
domain	B-Application
being	O
modeled	O
,	O
and	O
the	O
dependencies	O
it	O
has	O
on	O
other	O
domains	O
.	O
</s>
<s>
The	O
class	O
diagram	O
defines	O
the	O
classes	O
and	O
class	O
associations	O
for	O
the	O
domain	B-Application
.	O
</s>
<s>
The	O
statechart	B-Application
diagram	I-Application
defines	O
the	O
states	O
,	O
events	O
,	O
and	O
state	B-Architecture
transitions	O
for	O
a	O
class	O
or	O
class	O
instance	O
.	O
</s>
<s>
The	O
action	B-Language
language	I-Language
defines	O
the	O
actions	O
or	O
operations	O
that	O
perform	O
processing	O
on	O
model	O
elements	O
.	O
</s>
<s>
Executable	B-Language
UML	I-Language
requires	O
identification	O
of	O
the	O
domains	O
(	O
also	O
known	O
as	O
:	O
aspects	O
or	O
concerns	O
)	O
of	O
the	O
system	B-Application
.	O
</s>
<s>
"	O
Each	O
domain	B-Application
is	O
an	O
autonomous	O
world	O
inhabited	O
by	O
conceptual	O
entities	O
"	O
Each	O
domain	B-Application
can	O
be	O
modeled	O
independent	O
of	O
the	O
other	O
domains	O
in	O
the	O
system	B-Application
,	O
enabling	O
a	O
separation	O
of	O
concerns	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
domains	O
for	O
an	O
automated	O
teller	O
system	B-Application
may	O
include	O
the	O
following	O
:	O
</s>
<s>
The	O
application	O
domain	B-Application
model	O
of	O
the	O
automated	O
teller	O
's	O
business	B-Architecture
logic	I-Architecture
.	O
</s>
<s>
The	O
security	O
domain	B-Application
model	O
of	O
various	O
issues	O
regarding	O
system	B-Application
security	O
(	O
such	O
as	O
authentication	O
and	O
encryption	O
)	O
.	O
</s>
<s>
The	O
data	B-General_Concept
access	O
domain	B-Application
model	O
of	O
methods	O
for	O
external	O
data	B-General_Concept
usage	O
.	O
</s>
<s>
The	O
logging	O
domain	B-Application
model	O
of	O
the	O
various	O
methods	O
through	O
which	O
the	O
system	B-Application
can	O
or	O
must	O
log	O
information	O
.	O
</s>
<s>
The	O
user	B-Application
interface	I-Application
domain	B-Application
model	O
of	O
the	O
user	O
interactions	O
with	O
the	O
system	B-Application
.	O
</s>
<s>
The	O
architecture	B-Device
domain	B-Application
model	O
of	O
the	O
implemented	O
of	O
the	O
Executable	B-Language
UML	I-Language
model	O
on	O
the	O
system	B-Application
's	O
hardware	B-Architecture
and	O
software	B-Device
platforms	I-Device
.	O
</s>
<s>
The	O
separation	O
of	O
concerns	O
enables	O
each	O
domain	B-Application
to	O
be	O
developed	O
and	O
verified	O
independently	O
of	O
the	O
other	O
domains	O
in	O
the	O
system	B-Application
by	O
the	O
respective	O
domain	B-Application
experts	O
.	O
</s>
<s>
It	O
is	O
recommended	O
that	O
bridges	O
are	O
agreed	O
upon	O
by	O
the	O
different	O
domain	B-Application
experts	O
.	O
</s>
<s>
A	O
domain	B-Application
can	O
be	O
marked	O
as	O
realized	O
to	O
indicate	O
that	O
the	O
domain	B-Application
exists	O
and	O
does	O
not	O
need	O
to	O
be	O
modeled	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
data	B-General_Concept
access	O
domain	B-Application
that	O
uses	O
a	O
MySQL	B-Application
database	O
would	O
be	O
marked	O
as	O
realized	O
.	O
</s>
<s>
Conceptual	O
entities	O
,	O
such	O
as	O
tangible	O
things	O
,	O
roles	O
,	O
incidents	O
,	O
interactions	O
,	O
and	O
specifications	O
,	O
specific	O
to	O
the	O
domain	B-Application
being	O
modeled	O
are	O
abstracted	O
into	O
classes	O
.	O
</s>
<s>
An	O
association	B-Application
may	O
require	O
further	O
abstraction	B-Application
as	O
an	O
Association	B-Application
Class	O
.	O
</s>
<s>
Constraints	O
on	O
the	O
class	O
diagram	O
can	O
be	O
written	O
in	O
both	O
Action	B-Language
Language	I-Language
and	O
Object	B-Language
Constraint	I-Language
Language	I-Language
(	O
OCL	O
)	O
.	O
</s>
<s>
The	O
Executable	B-Language
UML	I-Language
method	O
limits	O
the	O
UML	B-Language
elements	O
that	O
can	O
be	O
used	O
in	O
an	O
Executable	B-Language
UML	I-Language
class	O
diagram	O
.	O
</s>
<s>
An	O
Executable	B-Language
UML	I-Language
class	O
diagram	O
is	O
meant	O
to	O
expose	O
information	O
about	O
the	O
domain	B-Application
.	O
</s>
<s>
Too	O
much	O
complexity	O
in	O
the	O
statechart	B-Application
diagrams	O
is	O
a	O
good	O
indicator	O
that	O
the	O
class	O
diagram	O
should	O
be	O
reworked	O
.	O
</s>
<s>
Classes	O
have	O
lifecycles	O
which	O
are	O
modeled	O
in	O
Executable	B-Language
UML	I-Language
with	O
a	O
statechart	B-Application
diagram	I-Application
.	O
</s>
<s>
The	O
statechart	B-Application
diagram	I-Application
defines	O
the	O
states	O
,	O
transitions	O
,	O
events	O
,	O
and	O
procedures	O
that	O
define	O
a	O
class	O
 '	O
behaviour	O
.	O
</s>
<s>
Each	O
state	B-Architecture
has	O
only	O
one	O
procedure	O
that	O
is	O
executed	O
upon	O
entry	B-General_Concept
into	I-General_Concept
that	I-General_Concept
state	I-General_Concept
.	O
</s>
<s>
A	O
procedure	O
is	O
composed	O
of	O
actions	O
,	O
which	O
are	O
specified	O
in	O
an	O
action	B-Language
language	I-Language
.	O
</s>
<s>
The	O
class	O
and	O
state	B-Architecture
models	O
by	O
themselves	O
can	O
only	O
provide	O
a	O
static	O
view	O
of	O
the	O
domain	B-Application
.	O
</s>
<s>
In	O
order	O
to	O
have	O
an	O
executable	O
model	O
,	O
there	O
must	O
be	O
a	O
way	O
to	O
create	O
class	O
instances	O
,	O
establish	O
associations	O
,	O
perform	O
operations	O
on	O
attributes	O
,	O
call	O
state	B-Architecture
events	O
,	O
etc	O
.	O
</s>
<s>
In	O
Executable	B-Language
UML	I-Language
,	O
this	O
is	O
done	O
using	O
an	O
action	B-Language
language	I-Language
that	O
conforms	O
to	O
the	O
UML	B-Language
Action	I-Language
Semantics	O
.	O
</s>
<s>
Action	O
Semantics	O
was	O
added	O
to	O
the	O
UML	B-Language
specification	O
in	O
2001	O
.	O
</s>
<s>
Existing	O
action	O
languages	O
are	O
Object	O
Action	B-Language
Language	I-Language
(	O
OAL	O
)	O
,	O
Shlaer	O
–	O
Mellor	O
Action	B-Language
Language	I-Language
(	O
SMALL	O
)	O
,	O
Action	O
Specification	O
Language	O
(	O
ASL	O
)	O
,	O
Model	O
Action	O
Specification	O
Language	O
(	O
MASL	O
)	O
,	O
That	O
Action	B-Language
Language	I-Language
(	O
TALL	O
)	O
,	O
Starr	O
's	O
Concise	O
Relational	O
Action	B-Language
Language	I-Language
(	O
SCRALL	O
)	O
,	O
Platform-independent	B-Operating_System
Action	B-Language
Language	I-Language
(	O
PAL	O
)	O
and	O
PathMATE	O
Action	B-Language
Language	I-Language
(	O
PAL	O
)	O
.	O
</s>
<s>
SCRALL	O
is	O
the	O
only	O
one	O
that	O
is	O
a	O
graphical	O
action	B-Language
language	I-Language
.	O
</s>
<s>
Once	O
a	O
domain	B-Application
is	O
modeled	O
,	O
it	O
can	O
be	O
tested	O
independent	O
of	O
the	O
target	O
implementation	O
by	O
executing	O
the	O
model	O
.	O
</s>
<s>
Each	O
domain	B-Application
can	O
be	O
verified	B-Application
and	I-Application
validated	I-Application
independent	O
of	O
any	O
other	O
domain	B-Application
.	O
</s>
<s>
This	O
allows	O
errors	O
detected	O
to	O
be	O
associated	O
with	O
the	O
domain	B-Application
and	O
independent	O
of	O
other	O
system	B-Application
concerns	O
.	O
</s>
<s>
Verification	O
will	O
involve	O
such	O
things	O
as	O
human	O
review	O
of	O
the	O
models	O
,	O
performed	O
by	O
experts	O
in	O
the	O
relevant	O
domain	B-Application
,	O
and	O
automated	O
checking	O
of	O
the	O
Executable	B-Language
UML	I-Language
semantics	O
.	O
</s>
<s>
i.e.	O
,	O
checking	O
that	O
the	O
Executable	B-Language
UML	I-Language
model	O
complies	O
with	O
the	O
Executable	B-Language
UML	I-Language
metamodel	O
.	O
</s>
<s>
Validation	O
will	O
typically	O
involve	O
use	O
of	O
an	O
Executable	B-Language
UML	I-Language
tool	O
to	O
execute	O
the	O
model	O
.	O
</s>
<s>
The	O
execution	O
can	O
occur	O
either	O
before	O
or	O
after	O
model	O
compilation	B-Language
.	O
</s>
<s>
In	O
order	O
to	O
support	O
execution	O
on	O
the	O
target	O
implementation	O
,	O
the	O
domain	B-Application
model	O
must	O
be	O
translated	O
into	O
a	O
less	O
abstract	B-Application
form	O
.	O
</s>
<s>
This	O
translation	O
process	O
is	O
called	O
model	O
compilation	B-Language
.	O
</s>
<s>
Most	O
model	O
compilers	B-Language
target	O
a	O
known	O
programming	O
language	O
,	O
because	O
this	O
allows	O
reuse	O
of	O
existing	O
compiler	B-Language
technologies	O
.	O
</s>
<s>
Optimizing	O
the	O
domain	B-Application
models	O
for	O
target	O
implementation	O
reasons	O
will	O
reduce	O
the	O
level	O
of	O
abstraction	B-Application
,	O
adversely	O
affect	O
domain	B-Application
independence	O
,	O
and	O
increase	O
the	O
cost	O
of	O
reuse	O
.	O
</s>
<s>
In	O
executable	B-Language
UML	I-Language
,	O
optimizations	O
are	O
done	O
by	O
the	O
model	O
compiler	B-Language
either	O
automatically	O
or	O
through	O
marking	O
.	O
</s>
<s>
Marking	O
allows	O
specific	O
model	O
elements	O
to	O
be	O
targeted	O
for	O
specific	O
lower-level	O
implementations	O
,	O
and	O
allows	O
for	O
broader	O
architectural	O
decisions	O
,	O
such	O
as	O
specifying	O
that	O
collections	O
of	O
objects	O
should	O
be	O
implemented	O
as	O
a	O
doubly	B-Data_Structure
linked	I-Data_Structure
list	I-Data_Structure
.	O
</s>
<s>
In	O
MDA	B-Architecture
terms	O
,	O
the	O
model	O
compiler	B-Language
creates	O
the	O
PSM	B-Architecture
.	O
</s>
<s>
The	O
separation	O
between	O
the	O
PIM	B-Architecture
and	O
PSM	B-Architecture
in	O
Executable	B-Language
UML	I-Language
disables	O
the	O
ability	O
to	O
round-trip	B-Application
engineer	I-Application
the	O
model	O
,	O
and	O
deters	O
modifications	O
to	O
the	O
PSM	B-Architecture
.	O
</s>
<s>
Executable	B-Language
UML	I-Language
defines	O
execution	O
semantics	O
for	O
a	O
subset	O
of	O
the	O
UML	B-Language
.	O
</s>
<s>
Key	O
aspects	O
of	O
the	O
Executable	B-Language
UML	I-Language
subset	O
include	O
the	O
following	O
:	O
</s>
<s>
Multiplicities	O
on	O
association	B-Application
ends	O
are	O
restricted	O
to	O
0	O
..	O
1	O
(	O
zero	O
to	O
one	O
)	O
,	O
*	O
(	O
zero	O
to	O
many	O
)	O
,	O
1	O
(	O
exactly	O
one	O
)	O
,	O
or	O
1	O
..	O
(	O
one	O
to	O
many	O
)	O
.	O
</s>
<s>
Data	B-General_Concept
types	O
are	O
restricted	O
to	O
the	O
following	O
core	O
data	B-General_Concept
types	O
:	O
boolean	O
,	O
string	O
,	O
integer	O
,	O
real	O
,	O
date	O
,	O
timestamp	O
,	O
and	O
arbitrary_id	O
,	O
or	O
one	O
of	O
the	O
following	O
domain-specific	O
data	B-General_Concept
types	O
:	O
numeric	O
,	O
string	O
,	O
enumerated	O
,	O
and	O
composite	O
.	O
</s>
<s>
Domain-specific	O
numeric	O
and	O
string	O
data	B-General_Concept
types	O
can	O
represent	O
subsets	O
of	O
the	O
core	O
data	B-General_Concept
types	O
.	O
</s>
<s>
The	O
domain-specific	O
composite	O
data	B-General_Concept
type	O
is	O
to	O
always	O
be	O
treated	O
as	O
a	O
single	O
unit	O
within	O
the	O
domain	B-Application
.	O
</s>
<s>
e.g.	O
,	O
a	O
MailingAddress	O
composite	O
data	B-General_Concept
type	O
could	O
be	O
declared	O
,	O
but	O
city	O
information	O
could	O
n't	O
be	O
extracted	O
from	O
it	O
.	O
</s>
<s>
Constraints	O
on	O
the	O
Executable	B-Language
UML	I-Language
models	O
can	O
either	O
be	O
represented	O
as	O
Object	B-Language
Constraint	I-Language
Language	I-Language
(	O
OCL	O
)	O
or	O
action	B-Language
language	I-Language
.	O
</s>
<s>
The	O
Object	B-Architecture
Management	I-Architecture
Group	I-Architecture
has	O
standardized	O
the	O
Foundational	O
UML	B-Language
(	O
fUML	O
)	O
,	O
which	O
was	O
strongly	O
influenced	O
by	O
Executable	B-Language
UML	I-Language
.	O
</s>
<s>
Action	B-Language
Language	I-Language
for	O
Foundational	O
UML	B-Language
(	O
ALF	O
)	O
,	O
is	O
a	O
standard	O
action	B-Language
language	I-Language
specification	O
by	O
the	O
Object	B-Architecture
Management	I-Architecture
Group	I-Architecture
.	O
</s>
