<s>
Open	B-Architecture
systems	I-Architecture
architecture	I-Architecture
is	O
a	O
system	O
design	O
approach	O
which	O
aims	O
to	O
produce	O
systems	O
that	O
are	O
inherently	O
interoperable	O
and	O
connectable	O
without	O
recourse	O
to	O
retrofit	O
and	O
redesign	O
.	O
</s>
<s>
In	O
open	B-Architecture
systems	I-Architecture
architecture	I-Architecture
,	O
the	O
design	O
includes	O
intentional	O
provisions	O
to	O
make	O
it	O
possible	O
to	O
expand	O
or	O
modify	O
the	O
system	O
at	O
a	O
later	O
stage	O
after	O
initial	O
operation	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
information	O
technology	O
and	O
telecommunication	O
,	O
such	O
design	O
principles	O
lead	O
to	O
open	B-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
In	O
telecommunication	O
,	O
open	B-Architecture
systems	I-Architecture
architecture	I-Architecture
(	O
OSA	O
)	O
is	O
a	O
standard	O
that	O
describes	O
the	O
layered	O
hierarchical	O
structure	O
,	O
configuration	B-General_Concept
,	O
or	O
model	O
of	O
a	O
communications	O
or	O
distributed	O
data	B-General_Concept
processing	I-General_Concept
system	O
.	O
</s>
<s>
It	O
enables	O
system	O
description	O
,	O
design	O
,	O
development	O
,	O
installation	O
,	O
operation	O
,	O
improvement	O
,	O
and	O
maintenance	O
to	O
be	O
performed	O
at	O
the	O
abstraction	B-Architecture
layers	I-Architecture
in	O
the	O
hierarchical	O
structure	O
.	O
</s>
<s>
Examples	O
of	O
independent	O
alterations	O
include	O
the	O
conversion	O
from	O
wire	O
to	O
optical	O
fiber	O
at	O
a	O
physical	B-Application
layer	I-Application
without	O
affecting	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
or	O
the	O
network	B-Application
layer	I-Application
,	O
except	O
to	O
provide	O
more	O
traffic	O
capacity	O
,	O
and	O
the	O
altering	O
of	O
the	O
operational	O
protocols	O
at	O
the	O
network	O
level	O
without	O
altering	O
the	O
physical	B-Application
layer	I-Application
.	O
</s>
