<s>
A	O
system	B-Architecture
architecture	I-Architecture
is	O
the	O
conceptual	B-Application
model	I-Application
that	O
defines	O
the	O
structure	O
,	O
behavior	O
,	O
and	O
more	O
views	B-Architecture
of	O
a	O
system	O
.	O
</s>
<s>
A	O
system	B-Architecture
architecture	I-Architecture
can	O
consist	O
of	O
system	O
components	O
and	O
the	O
sub-systems	O
developed	O
,	O
that	O
will	O
work	O
together	O
to	O
implement	O
the	O
overall	O
system	O
.	O
</s>
<s>
There	O
have	O
been	O
efforts	O
to	O
formalize	O
languages	O
to	O
describe	O
system	B-Architecture
architecture	I-Architecture
,	O
collectively	O
these	O
are	O
called	O
architecture	B-Architecture
description	I-Architecture
languages	I-Architecture
(	O
ADLs	O
)	O
.	O
</s>
<s>
Various	O
organizations	O
can	O
define	O
systems	B-Architecture
architecture	I-Architecture
in	O
different	O
ways	O
,	O
including	O
:	O
</s>
<s>
A	O
representation	O
of	O
a	O
system	O
,	O
including	O
a	O
mapping	O
of	O
functionality	O
onto	O
hardware	O
and	O
software	O
components	O
,	O
a	O
mapping	O
of	O
the	O
software	B-Architecture
architecture	I-Architecture
onto	O
the	O
hardware	O
architecture	O
,	O
and	O
human	O
interaction	O
with	O
these	O
components	O
.	O
</s>
<s>
One	O
can	O
think	O
of	O
system	B-Architecture
architecture	I-Architecture
as	O
a	O
set	O
of	O
representations	O
of	O
an	O
existing	O
(	O
or	O
future	O
)	O
system	O
.	O
</s>
<s>
System	B-Architecture
architecture	I-Architecture
conveys	O
the	O
informational	O
content	O
of	O
the	O
elements	O
consisting	O
of	O
a	O
system	O
,	O
the	O
relationships	O
among	O
those	O
elements	O
,	O
and	O
the	O
rules	O
governing	O
those	O
relationships	O
.	O
</s>
<s>
A	O
system	B-Architecture
architecture	I-Architecture
primarily	O
concentrates	O
on	O
the	O
internal	O
interfaces	B-Application
among	O
the	O
system	O
's	O
components	O
or	O
subsystems	O
,	O
and	O
on	O
the	O
interface(s )	O
between	O
the	O
system	O
and	O
its	O
external	O
environment	O
,	O
especially	O
the	O
user	O
.	O
</s>
<s>
(	O
In	O
the	O
specific	O
case	O
of	O
computer	O
systems	O
,	O
this	O
latter	O
,	O
special	O
,	O
interface	B-Application
is	O
known	O
as	O
the	O
computer	B-Application
human	I-Application
interface	I-Application
,	O
AKA	O
human	O
computer	B-Application
interface	I-Application
,	O
or	O
HCI	O
;	O
formerly	O
called	O
the	O
man-machine	B-Application
interface	I-Application
.	O
)	O
</s>
<s>
One	O
can	O
contrast	O
a	O
system	B-Architecture
architecture	I-Architecture
with	O
system	B-Architecture
architecture	I-Architecture
engineering	O
(	O
SAE	O
)	O
-	O
the	O
method	O
and	O
discipline	O
for	O
effectively	O
implementing	O
the	O
architecture	O
of	O
a	O
system	O
:	O
</s>
<s>
SAE	O
is	O
a	O
method	O
because	O
a	O
sequence	O
of	O
steps	O
is	O
prescribed	O
to	O
produce	O
or	O
to	O
change	O
the	O
architecture	O
of	O
a	O
system	O
within	O
a	O
set	O
of	O
constraints	B-Application
.	O
</s>
<s>
SAE	O
is	O
a	O
discipline	O
because	O
a	O
body	O
of	O
knowledge	O
is	O
used	O
to	O
inform	O
practitioners	O
as	O
to	O
the	O
most	O
effective	O
way	O
to	O
design	O
the	O
system	O
within	O
a	O
set	O
of	O
constraints	B-Application
.	O
</s>
<s>
Systems	B-Architecture
architecture	I-Architecture
depends	O
heavily	O
on	O
practices	O
and	O
techniques	O
which	O
were	O
developed	O
over	O
thousands	O
of	O
years	O
in	O
many	O
other	O
fields	O
,	O
perhaps	O
the	O
most	O
important	O
being	O
civil	O
architecture	O
.	O
</s>
<s>
However	O
,	O
with	O
the	O
arrival	O
of	O
digital	O
computers	O
and	O
the	O
development	O
of	O
software	B-General_Concept
engineering	I-General_Concept
as	O
a	O
separate	O
discipline	O
,	O
it	O
was	O
often	O
necessary	O
to	O
distinguish	O
among	O
engineered	O
hardware	O
artifacts	O
,	O
software	O
artifacts	O
,	O
and	O
the	O
combined	O
artifacts	O
.	O
</s>
<s>
A	O
programmable	B-Application
hardware	O
artifact	O
,	O
or	O
computing	O
machine	O
,	O
that	O
lacks	O
its	O
computer	B-Application
program	I-Application
is	O
impotent	O
;	O
even	O
as	O
a	O
software	O
artifact	O
,	O
or	O
program	O
,	O
is	O
equally	O
impotent	O
unless	O
it	O
can	O
be	O
used	O
to	O
alter	O
the	O
sequential	O
states	O
of	O
a	O
suitable	O
(	O
hardware	O
)	O
machine	O
.	O
</s>
<s>
Within	O
the	O
computer	O
and	O
software	B-General_Concept
engineering	I-General_Concept
disciplines	O
(	O
and	O
,	O
often	O
,	O
other	O
engineering	O
disciplines	O
,	O
such	O
as	O
communications	O
)	O
,	O
then	O
,	O
the	O
term	O
system	O
came	O
to	O
be	O
defined	O
as	O
containing	O
all	O
of	O
the	O
elements	O
necessary	O
(	O
which	O
generally	O
includes	O
both	O
hardware	O
and	O
software	O
)	O
to	O
perform	O
a	O
useful	O
function	O
.	O
</s>
<s>
Consequently	O
,	O
within	O
these	O
engineering	O
disciplines	O
,	O
a	O
system	O
generally	O
refers	O
to	O
a	O
programmable	B-Application
hardware	O
machine	O
and	O
its	O
included	O
program	O
.	O
</s>
<s>
And	O
a	O
systems	O
engineer	O
is	O
defined	O
as	O
one	O
concerned	O
with	O
the	O
complete	O
device	O
,	O
both	O
hardware	O
and	O
software	O
and	O
,	O
more	O
particularly	O
,	O
all	O
of	O
the	O
interfaces	B-Application
of	O
the	O
device	O
,	O
including	O
that	O
between	O
hardware	O
and	O
software	O
,	O
and	O
especially	O
between	O
the	O
complete	O
device	O
and	O
its	O
user	O
(	O
the	O
CHI	O
)	O
.	O
</s>
<s>
The	O
hardware	O
engineer	O
deals	O
(	O
more	O
or	O
less	O
)	O
exclusively	O
with	O
the	O
hardware	O
device	O
;	O
the	O
software	B-General_Concept
engineer	I-General_Concept
deals	O
(	O
more	O
or	O
less	O
)	O
exclusively	O
with	O
the	O
computer	B-Application
program	I-Application
;	O
and	O
the	O
systems	O
engineer	O
is	O
responsible	O
for	O
seeing	O
that	O
the	O
program	O
is	O
capable	O
of	O
properly	O
running	O
within	O
the	O
hardware	O
device	O
,	O
and	O
that	O
the	O
system	O
composed	O
of	O
the	O
two	O
entities	O
is	O
capable	O
of	O
properly	O
interacting	O
with	O
its	O
external	O
environment	O
,	O
especially	O
the	O
user	O
,	O
and	O
performing	O
its	O
intended	O
function	O
.	O
</s>
<s>
A	O
systems	B-Architecture
architecture	I-Architecture
makes	O
use	O
of	O
elements	O
of	O
both	O
software	O
and	O
hardware	O
and	O
is	O
used	O
to	O
enable	O
design	O
of	O
such	O
a	O
composite	O
system	O
.	O
</s>
<s>
A	O
good	O
architecture	O
may	O
be	O
viewed	O
as	O
a	O
'	O
partitioning	O
scheme	O
,	O
'	O
or	O
algorithm	O
,	O
which	O
partitions	O
all	O
of	O
the	O
system	O
's	O
present	O
and	O
foreseeable	O
requirements	O
into	O
a	O
workable	O
set	O
of	O
cleanly	O
bounded	B-Algorithm
subsystems	O
with	O
nothing	O
left	O
over	O
.	O
</s>
<s>
Moreover	O
,	O
a	O
good	O
architecture	O
provides	O
for	O
an	O
easy	O
mapping	O
to	O
the	O
user	O
's	O
requirements	O
and	O
the	O
validation	B-Application
tests	I-Application
of	O
the	O
user	O
's	O
requirements	O
.	O
</s>
<s>
Several	O
types	O
of	O
systems	B-Architecture
architectures	I-Architecture
(	O
underlain	O
by	O
the	O
same	O
fundamental	O
principles	O
)	O
have	O
been	O
identified	O
as	O
follows	O
:	O
</s>
