<s>
A	O
data-flow	B-Application
diagram	I-Application
is	O
a	O
way	O
of	O
representing	O
a	O
flow	B-Application
of	I-Application
data	I-Application
through	O
a	O
process	O
or	O
a	O
system	O
(	O
usually	O
an	O
information	O
system	O
)	O
.	O
</s>
<s>
A	O
data-flow	B-Application
diagram	I-Application
has	O
no	O
control	O
are	O
no	O
decision	O
rules	O
and	O
no	O
loops	O
.	O
</s>
<s>
Specific	O
operations	O
based	O
on	O
the	O
data	O
can	O
be	O
represented	O
by	O
a	O
flowchart	B-Language
.	O
</s>
<s>
There	O
are	O
several	O
notations	O
for	O
displaying	O
data-flow	B-Application
diagrams	I-Application
.	O
</s>
<s>
For	O
each	O
data	B-Application
flow	I-Application
,	O
at	O
least	O
one	O
of	O
the	O
endpoints	O
(	O
source	O
and	O
/	O
or	O
destination	O
)	O
must	O
exist	O
in	O
a	O
process	O
.	O
</s>
<s>
The	O
refined	O
representation	O
of	O
a	O
process	O
can	O
be	O
done	O
in	O
another	O
data-flow	B-Application
diagram	I-Application
,	O
which	O
subdivides	O
this	O
process	O
into	O
sub-processes	O
.	O
</s>
<s>
The	O
data-flow	B-Application
diagram	I-Application
is	O
a	O
tool	O
that	O
is	O
part	O
of	O
structured	O
analysis	O
and	O
data	B-Application
modeling	I-Application
.	O
</s>
<s>
When	O
using	O
UML	B-Language
,	O
the	O
activity	O
diagram	O
typically	O
takes	O
over	O
the	O
role	O
of	O
the	O
data-flow	B-Application
diagram	I-Application
.	O
</s>
<s>
A	O
special	O
form	O
of	O
data-flow	B-Application
plan	O
is	O
a	O
site-oriented	O
data-flow	B-Application
plan	O
.	O
</s>
<s>
Data-flow	B-Application
diagrams	I-Application
can	O
be	O
regarded	O
as	O
inverted	O
Petri	B-Operating_System
nets	I-Operating_System
,	O
because	O
places	O
in	O
such	O
networks	O
correspond	O
to	O
the	O
semantics	O
of	O
data	O
memories	O
.	O
</s>
<s>
Analogously	O
,	O
the	O
semantics	O
of	O
transitions	O
from	O
Petri	B-Operating_System
nets	I-Operating_System
and	O
data	B-Application
flows	I-Application
and	O
functions	O
from	O
data-flow	B-Application
diagrams	I-Application
should	O
be	O
considered	O
equivalent	O
.	O
</s>
<s>
The	O
DFD	O
notation	O
draws	O
on	O
graph	O
theory	O
,	O
originally	O
used	O
in	O
operational	O
research	O
to	O
model	O
workflow	B-Operating_System
in	O
organizations	O
.	O
</s>
<s>
Data-flow	B-Application
diagrams	I-Application
(	O
DFD	O
)	O
quickly	O
became	O
a	O
popular	O
way	O
to	O
visualize	O
the	O
major	O
steps	O
and	O
data	O
involved	O
in	O
software-system	O
processes	O
.	O
</s>
<s>
DFDs	O
were	O
usually	O
used	O
to	O
show	O
data	B-Application
flow	I-Application
in	O
a	O
computer	O
system	O
,	O
although	O
they	O
could	O
in	O
theory	O
be	O
applied	O
to	O
business	O
process	O
modeling	O
.	O
</s>
<s>
DFDs	O
were	O
useful	O
to	O
document	O
the	O
major	O
data	B-Application
flows	I-Application
or	O
to	O
explore	O
a	O
new	O
high-level	O
design	O
in	O
terms	O
of	O
data	B-Application
flow	I-Application
.	O
</s>
<s>
Data	B-Application
flow	I-Application
(	O
flow	O
,	O
dataflow	B-Application
)	O
shows	O
the	O
transfer	O
of	O
information	O
(	O
sometimes	O
also	O
material	O
)	O
from	O
one	O
part	O
of	O
the	O
system	O
to	O
another	O
.	O
</s>
<s>
The	O
warehouse	O
is	O
represented	O
by	O
two	O
parallel	O
lines	O
between	O
which	O
the	O
memory	O
name	O
is	O
located	O
(	O
it	O
can	O
be	O
modeled	O
as	O
a	O
UML	B-Language
buffer	O
node	O
)	O
.	O
</s>
<s>
The	O
Terminator	O
is	O
an	O
external	B-Application
entity	I-Application
that	O
communicates	O
with	O
the	O
system	O
and	O
stands	O
outside	O
of	O
the	O
system	O
.	O
</s>
<s>
DFD	O
must	O
be	O
consistent	O
with	O
other	O
models	O
of	O
the	O
system	O
-	O
entity	B-Architecture
relationship	I-Architecture
diagram	I-Architecture
,	O
state-transition	B-Application
diagram	I-Application
,	O
data	B-Application
dictionary	I-Application
,	O
and	O
process	O
specification	O
models	O
.	O
</s>
