<s>
A	O
diagram	O
is	O
a	O
symbolic	O
representation	O
of	O
information	O
using	O
visualization	B-Application
techniques	O
.	O
</s>
<s>
Diagrams	B-Application
have	O
been	O
used	O
since	O
prehistoric	O
times	O
on	O
walls	O
of	O
caves	O
,	O
but	O
became	O
more	O
prevalent	O
during	O
the	O
Enlightenment	O
.	O
</s>
<s>
Sometimes	O
,	O
the	O
technique	O
uses	O
a	O
three-dimensional	O
visualization	B-Application
which	O
is	O
then	O
projected	B-Algorithm
onto	O
a	O
two-dimensional	O
surface	O
.	O
</s>
<s>
The	O
word	O
graph	O
is	O
sometimes	O
used	O
as	O
a	O
synonym	B-Application
for	O
diagram	O
.	O
</s>
<s>
visual	O
information	O
device	O
:	O
Like	O
the	O
term	O
"	O
illustration	O
"	O
,	O
"	O
diagram	O
"	O
is	O
used	O
as	O
a	O
collective	O
term	O
standing	O
for	O
the	O
whole	O
class	O
of	O
technical	O
genres	O
,	O
including	O
graphs	O
,	O
technical	B-Application
drawings	I-Application
and	O
tables	O
.	O
</s>
<s>
For	O
example	O
,	O
Anderson	O
(	O
1997	O
)	O
stated	O
more	O
generally	O
:	O
"	O
diagrams	B-Application
are	O
pictorial	O
,	O
yet	O
abstract	O
,	O
representations	O
of	O
information	O
,	O
and	O
maps	O
,	O
line	O
graphs	O
,	O
bar	B-Application
charts	I-Application
,	O
engineering	O
blueprints	B-Application
,	O
and	O
architects	B-Application
 '	O
sketches	O
are	O
all	O
examples	O
of	O
diagrams	B-Application
,	O
whereas	O
photographs	O
and	O
video	O
are	O
not	O
"	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
Lowe	O
(	O
1993	O
)	O
defined	O
diagrams	B-Application
as	O
specifically	O
"	O
abstract	O
graphic	O
portrayals	O
of	O
the	O
subject	O
matter	O
they	O
represent	O
"	O
.	O
</s>
<s>
In	O
the	O
specific	O
sense	O
diagrams	B-Application
and	O
charts	O
contrast	O
with	O
computer	O
graphics	O
,	O
technical	O
illustrations	O
,	O
infographics	O
,	O
maps	O
,	O
and	O
technical	B-Application
drawings	I-Application
,	O
by	O
showing	O
"	O
abstract	O
rather	O
than	O
literal	O
representations	O
of	O
information	O
"	O
.	O
</s>
<s>
Or	O
in	O
Hall	O
's	O
(	O
1996	O
)	O
words	O
"	O
diagrams	B-Application
are	O
simplified	O
figures	O
,	O
caricatures	O
in	O
a	O
way	O
,	O
intended	O
to	O
convey	O
essential	O
meaning	O
"	O
.	O
</s>
<s>
Diagrammatology	B-Application
is	O
the	O
academic	O
study	O
of	O
diagrams	B-Application
.	O
</s>
<s>
Rather	O
a	O
diagram	O
may	O
only	O
have	O
structural	B-Algorithm
similarity	I-Algorithm
to	O
what	O
it	O
represents	O
,	O
an	O
idea	O
often	O
attributed	O
to	O
Charles	O
Sanders	O
Peirce	O
.	O
</s>
<s>
Structural	B-Algorithm
similarity	I-Algorithm
can	O
be	O
defined	O
in	O
terms	O
of	O
a	O
mapping	O
between	O
parts	O
of	O
the	O
diagram	O
and	O
parts	O
of	O
what	O
the	O
diagram	O
represents	O
and	O
the	O
properties	O
of	O
this	O
mapping	O
,	O
such	O
as	O
maintaining	O
relations	O
between	O
these	O
parts	O
and	O
facts	O
about	O
these	O
relations	O
.	O
</s>
<s>
There	O
are	O
at	O
least	O
the	O
following	O
types	O
of	O
diagrams	B-Application
:	O
</s>
<s>
Logical	O
or	O
conceptual	O
diagrams	B-Application
,	O
which	O
take	O
a	O
collection	O
of	O
items	O
and	O
relationships	O
between	O
them	O
,	O
and	O
express	O
them	O
by	O
giving	O
each	O
item	O
a	O
2D	O
position	O
,	O
while	O
the	O
relationships	O
are	O
expressed	O
as	O
connections	O
between	O
the	O
items	O
or	O
overlaps	O
between	O
the	O
items	O
,	O
for	O
example	O
:	O
</s>
<s>
Quantitative	O
diagrams	B-Application
,	O
which	O
display	O
a	O
relationship	O
between	O
two	O
variables	O
that	O
take	O
either	O
discrete	O
or	O
a	O
continuous	O
range	O
of	O
values	O
;	O
for	O
example	O
:	O
</s>
<s>
Schematics	B-Application
and	O
other	O
types	O
of	O
diagrams	B-Application
,	O
for	O
example	O
:	O
</s>
<s>
Many	O
of	O
these	O
types	O
of	O
diagrams	B-Application
are	O
commonly	O
generated	O
using	O
diagramming	B-Application
software	O
such	O
as	O
Visio	B-Application
and	O
Gliffy	B-Application
.	O
</s>
<s>
Diagrams	B-Application
may	O
also	O
be	O
classified	O
according	O
to	O
use	O
or	O
purpose	O
,	O
for	O
example	O
,	O
explanatory	O
and/or	O
how	O
to	O
diagrams	B-Application
.	O
</s>
<s>
SDL/GR	B-Application
diagram	I-Application
–	O
specification	B-Application
and	I-Application
description	I-Application
Language	I-Application
.	O
</s>
<s>
SDL	O
is	O
a	O
formal	O
language	O
used	O
in	O
computer	B-General_Concept
science	I-General_Concept
.	O
</s>
