<s>
Real-Time	B-Application
Object-Oriented	I-Application
Modeling	I-Application
(	O
ROOM	O
)	O
is	O
a	O
domain-specific	B-Language
language	I-Language
.	O
</s>
<s>
ROOM	O
was	O
developed	O
in	O
the	O
early	O
1990s	O
for	O
modeling	O
Real-time	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
The	O
initial	O
focus	O
was	O
on	O
telecommunications	O
,	O
even	O
though	O
ROOM	O
can	O
be	O
applied	O
to	O
any	O
event-driven	O
real-time	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
When	O
UML2	O
was	O
defined	O
(	O
version	O
2	O
of	O
UML	B-Language
with	O
real	O
time	O
extensions	O
)	O
,	O
many	O
elements	O
of	O
ROOM	O
were	O
adopted	O
.	O
</s>
<s>
It	O
allows	O
the	O
complete	O
code	B-Application
generation	I-Application
for	O
the	O
whole	O
system	O
from	O
the	O
model	O
.	O
</s>
<s>
for	O
graphical	B-Application
user	I-Application
interfaces	I-Application
(	O
GUI	B-Application
)	O
.	O
</s>
<s>
ROOM	O
describes	O
a	O
software	O
system	O
along	O
three	O
dimensions	O
:	O
structure	O
,	O
behavior	O
and	O
inheritance	B-Language
.	O
</s>
<s>
Actors	O
do	O
exchange	B-Architecture
messages	I-Architecture
asynchronously	O
via	O
ports	O
and	O
bindings	O
.	O
</s>
<s>
An	O
actor	O
can	O
contain	O
other	O
actors	O
(	O
as	O
a	O
composition	B-Language
)	O
.	O
</s>
<s>
Each	O
actor	O
in	O
ROOM	O
has	O
a	O
behavior	O
which	O
is	O
defined	O
by	O
means	O
of	O
a	O
hierarchical	O
finite-state	B-Architecture
machine	I-Architecture
,	O
or	O
just	O
state	B-Architecture
machine	I-Architecture
for	O
short	O
.	O
</s>
<s>
A	O
state	B-Architecture
machine	I-Architecture
is	O
a	O
directed	O
graph	O
consisting	O
of	O
nodes	O
called	O
states	O
and	O
edges	O
called	O
transitions	O
.	O
</s>
<s>
If	O
a	O
transition	O
specifies	O
a	O
certain	O
trigger	O
then	O
it	O
is	O
said	O
to	O
fire	O
if	O
the	O
state	B-Architecture
machine	I-Architecture
is	O
in	O
the	O
source	O
state	O
of	O
the	O
transition	O
and	O
a	O
message	O
of	O
the	O
type	O
specified	O
by	O
the	O
trigger	O
arrives	O
.	O
</s>
<s>
In	O
ROOM	O
this	O
code	O
is	O
written	O
in	O
the	O
so	O
called	O
detail	O
level	O
language	O
,	O
usually	O
the	O
target	O
language	O
of	O
the	O
code	B-Application
generation	I-Application
.	O
</s>
<s>
State	B-Architecture
machines	I-Architecture
in	O
ROOM	O
also	O
have	O
a	O
graphical	O
notation	O
similar	O
to	O
the	O
UML	B-Application
state	I-Application
charts	I-Application
.	O
</s>
<s>
A	O
state	B-Architecture
machine	I-Architecture
can	O
also	O
have	O
a	O
hierarchy	O
in	O
the	O
sense	O
that	O
states	O
can	O
have	O
sub	O
state	B-Architecture
machines	I-Architecture
.	O
</s>
<s>
For	O
details	O
of	O
the	O
semantics	O
of	O
hierarchical	B-Application
state	I-Application
machines	I-Application
we	O
refer	O
to	O
the	O
original	O
book	O
.	O
</s>
<s>
An	O
important	O
concept	O
in	O
the	O
context	O
of	O
state	B-Architecture
machines	I-Architecture
is	O
the	O
execution	O
model	O
of	O
run-to-completion	O
.	O
</s>
<s>
But	O
after	O
a	O
short	O
while	O
of	O
getting	O
accustomed	O
it	O
will	O
be	O
evident	O
that	O
asynchronously	O
communicating	O
state	B-Architecture
machines	I-Architecture
are	O
perfectly	O
suited	O
for	O
control	O
software	O
.	O
</s>
<s>
Like	O
other	O
object	B-Language
oriented	I-Language
programming	I-Language
languages	I-Language
ROOM	O
uses	O
the	O
concept	O
of	O
classes	O
.	O
</s>
<s>
Actors	O
are	O
classes	O
which	O
can	O
be	O
instantiated	O
as	O
objects	B-Language
several	O
times	O
in	O
the	O
system	O
.	O
</s>
<s>
Similar	O
to	O
other	O
modern	O
programming	O
languages	O
ROOM	O
allows	O
inheritance	B-Language
of	O
actor	O
classes	O
.	O
</s>
<s>
It	O
is	O
a	O
single	O
inheritance	B-Language
as	O
an	O
actor	O
class	O
can	O
be	O
derived	O
from	O
another	O
actor	O
class	O
(	O
its	O
base	O
class	O
)	O
.	O
</s>
<s>
It	O
inherits	O
all	O
features	O
of	O
the	O
base	O
class	O
like	O
ports	O
and	O
actor	O
refs	O
,	O
but	O
also	O
the	O
state	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
This	O
concept	O
is	O
very	O
similar	O
to	O
dependency	B-Library
injection	I-Library
.	O
</s>
<s>
Bran	O
Selic	O
,	O
Garth	O
Gullekson	O
,	O
Paul	O
T	O
.	O
Ward	O
:	O
"	O
Real-Time	B-Application
Object-Oriented	I-Application
Modeling	I-Application
"	O
,	O
New	O
York	O
,	O
John	O
Wiley	O
&	O
Sons	O
Inc	O
,	O
1994	O
,	O
</s>
