<s>
Signal	B-Application
programming	I-Application
is	O
used	O
in	O
the	O
same	O
sense	O
as	O
dataflow	B-Application
programming	I-Application
,	O
and	O
is	O
similar	O
to	O
event-driven	B-Application
programming	I-Application
.	O
</s>
<s>
The	O
word	O
signal	B-Operating_System
is	O
used	O
instead	O
of	O
the	O
word	O
dataflow	B-Application
in	O
documentation	O
of	O
such	O
libraries	B-Library
as	O
Qt	B-Language
,	O
GTK+	B-Application
and	O
libsigc++	B-Language
.	O
</s>
<s>
The	O
time	O
instants	O
when	O
the	O
signal	B-Operating_System
value	O
(	O
or	O
dataflow	B-Application
value	O
)	O
changes	O
correspond	O
to	O
events	O
in	O
event-driven	B-Application
programming	I-Application
.	O
</s>
<s>
The	O
signal	B-Operating_System
flow	O
of	O
a	O
program	O
or	O
a	O
signal	B-Operating_System
processing	O
system	O
is	O
described	O
graphically	O
in	O
a	O
signal-flow	O
graph	O
or	O
a	O
data-flow	B-Application
diagram	I-Application
.	O
</s>
<s>
In	O
software	O
development	O
,	O
a	O
signal	B-Operating_System
can	O
mean	O
synchronous	O
events	O
(	O
sequences	O
of	O
samples	O
,	O
video	O
frames	O
,	O
etc.	O
,	O
with	O
constant	O
sample	O
rate	O
or	O
frame	O
rate	O
)	O
rather	O
than	O
asynchronous	B-Operating_System
events	O
,	O
while	O
the	O
word	O
event	O
and	O
data	B-Application
flow	I-Application
is	O
often	O
used	O
for	O
asynchronous	B-Operating_System
event	B-Operating_System
queues	I-Operating_System
,	O
but	O
this	O
is	O
by	O
no	O
means	O
universal	O
.	O
</s>
<s>
Especially	O
in	O
telecommunications	O
,	O
electrical	O
engineering	O
and	O
signal	B-Operating_System
processing	O
,	O
a	O
digital	O
signal	B-Operating_System
is	O
a	O
sampled	O
representation	O
of	O
an	O
analog	O
physical	O
entity	O
.	O
</s>
<s>
In	O
telecommunications	O
,	O
the	O
term	O
signalling	O
means	O
asynchronous	B-Operating_System
phone	O
call	O
metadata	O
information	O
exchange	O
,	O
for	O
example	O
of	O
telephone	O
numbers	O
.	O
</s>
<s>
One	O
application	O
of	O
synchronous	O
signal	B-Application
programming	I-Application
is	O
observer	B-Language
pattern	I-Language
.	O
</s>
<s>
In	O
databases	O
and	O
operational	O
systems	O
,	O
a	O
signal	B-Operating_System
is	O
a	O
sequence	O
or	O
flow	O
of	O
messages	O
within	O
a	O
message	O
passing	O
architecture	O
that	O
a	O
software	O
agent	O
can	O
subscribe	O
on	O
.	O
</s>
<s>
Note	O
that	O
these	O
signals	O
are	O
asynchronous	B-Operating_System
.	O
</s>
<s>
Also	O
signal	B-Application
programming	I-Application
is	O
used	O
in	O
a	O
narrow	O
sense	O
of	O
programming	O
with	O
Unix	B-Operating_System
signals	I-Operating_System
such	O
as	O
SIGTERM	B-General_Concept
,	O
SIGSEGV	B-Error_Name
,	O
SIGPOLL	B-General_Concept
etc	O
.	O
</s>
