<s>
A	O
block	B-Application
diagram	I-Application
is	O
a	O
diagram	O
of	O
a	O
system	O
in	O
which	O
the	O
principal	O
parts	O
or	O
functions	O
are	O
represented	O
by	O
blocks	O
connected	O
by	O
lines	O
that	O
show	O
the	O
relationships	O
of	O
the	O
blocks	O
.	O
</s>
<s>
Block	B-Application
diagrams	I-Application
are	O
typically	O
used	O
for	O
higher	O
level	O
,	O
less	O
detailed	O
descriptions	O
that	O
are	O
intended	O
to	O
clarify	O
overall	O
concepts	O
without	O
concern	O
for	O
the	O
details	O
of	O
implementation	O
.	O
</s>
<s>
Contrast	O
this	O
with	O
the	O
schematic	B-Application
diagrams	I-Application
and	O
layout	O
diagrams	O
used	O
in	O
electrical	O
engineering	O
,	O
which	O
show	O
the	O
implementation	O
details	O
of	O
electrical	O
components	O
and	O
physical	O
construction	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
a	O
block	B-Application
diagram	I-Application
of	O
a	O
radio	O
is	O
not	O
expected	O
to	O
show	O
each	O
and	O
every	O
connection	O
and	O
dial	O
and	O
switch	O
,	O
but	O
the	O
schematic	B-Application
diagram	I-Application
is	O
.	O
</s>
<s>
The	O
schematic	B-Application
diagram	I-Application
of	O
a	O
radio	O
does	O
not	O
show	O
the	O
width	O
of	O
each	O
connection	O
in	O
the	O
printed	O
circuit	O
board	O
,	O
but	O
the	O
layout	O
does	O
.	O
</s>
<s>
To	O
make	O
an	O
analogy	O
to	O
the	O
map	O
making	O
world	O
,	O
a	O
block	B-Application
diagram	I-Application
is	O
similar	O
to	O
a	O
highway	O
map	O
of	O
an	O
entire	O
nation	O
.	O
</s>
<s>
Block	B-Application
diagrams	I-Application
rely	O
on	O
the	O
principle	O
of	O
the	O
black	B-Device
box	I-Device
where	O
the	O
contents	O
are	O
hidden	O
from	O
view	O
either	O
to	O
avoid	O
being	O
distracted	O
by	O
the	O
details	O
or	O
because	O
the	O
details	O
are	O
not	O
known	O
.	O
</s>
<s>
In	O
electrical	O
engineering	O
,	O
a	O
design	O
will	O
often	O
begin	O
as	O
a	O
very	O
high	O
level	O
block	B-Application
diagram	I-Application
,	O
becoming	O
more	O
and	O
more	O
detailed	O
block	B-Application
diagrams	I-Application
as	O
the	O
design	O
progresses	O
,	O
finally	O
ending	O
in	O
block	B-Application
diagrams	I-Application
detailed	O
enough	O
that	O
each	O
individual	O
block	O
can	O
be	O
easily	O
implemented	O
(	O
at	O
which	O
point	O
the	O
block	B-Application
diagram	I-Application
is	O
also	O
a	O
schematic	B-Application
diagram	I-Application
)	O
.	O
</s>
<s>
Block	B-Application
diagrams	I-Application
are	O
used	O
in	O
every	O
discipline	O
of	O
engineering	O
.	O
</s>
<s>
In	O
process	O
control	O
,	O
block	B-Application
diagrams	I-Application
are	O
a	O
visual	O
language	O
for	O
describing	O
actions	O
in	O
a	O
complex	O
system	O
in	O
which	O
blocks	O
are	O
black	B-Device
boxes	I-Device
that	O
represent	O
mathematical	O
or	O
logical	O
operations	O
that	O
occur	O
in	O
sequence	O
from	O
left	O
to	O
right	O
and	O
top	O
to	O
bottom	O
,	O
but	O
not	O
the	O
physical	O
entities	O
,	O
such	O
as	O
processors	O
or	O
relays	O
,	O
that	O
perform	O
those	O
operations	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
create	O
such	O
block	B-Application
diagrams	I-Application
and	O
implement	O
their	O
functionality	O
with	O
specialized	O
programmable	O
logic	O
controller	O
(	O
PLC	O
)	O
programming	O
languages	O
.	O
</s>
<s>
There	O
is	O
some	O
similarity	O
between	O
the	O
block	B-Application
diagram	I-Application
and	O
what	O
is	O
called	O
Systems	O
Biology	O
Graphical	O
Notation	O
.	O
</s>
<s>
As	O
it	O
is	O
there	O
is	O
use	O
made	O
in	O
systems	O
biology	O
of	O
the	O
block	B-Application
diagram	I-Application
technique	O
harnessed	O
by	O
control	O
engineering	O
where	O
the	O
latter	O
is	O
itself	O
an	O
application	O
of	O
control	O
theory	O
.	O
</s>
<s>
An	O
example	O
of	O
this	O
is	O
the	O
function	B-Application
block	I-Application
diagram	I-Application
,	O
one	O
of	O
five	O
programming	O
languages	O
defined	O
in	O
part	O
3	O
of	O
the	O
IEC	O
61131	O
(	O
see	O
IEC	O
61131-3	O
)	O
standard	O
that	O
is	O
highly	O
formalized	O
(	O
see	O
formal	O
system	O
)	O
,	O
with	O
strict	O
rules	O
for	O
how	O
diagrams	O
are	O
to	O
be	O
built	O
.	O
</s>
