<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
suppose	O
we	O
have	O
a	O
data	O
item	O
A	O
whose	O
value	O
depends	O
on	O
data	O
item	O
B	O
,	O
i.e.	O
,	O
the	O
value	O
of	O
A	O
must	O
be	O
changed	O
after	O
the	O
value	O
of	O
B	O
changes	O
and	O
before	O
the	O
value	O
of	O
A	O
becomes	O
necessary	O
.	O
</s>
<s>
Active	B-General_Concept
updating	I-General_Concept
is	O
updating	O
A	O
immediately	O
after	O
B	O
changes	O
,	O
while	O
passive	O
updating	O
or	O
lazy	O
updating	O
(	O
lazy	O
evaluation	O
)	O
is	O
updating	O
A	O
immediately	O
before	O
its	O
value	O
is	O
fetched	O
.	O
</s>
<s>
And	O
example	O
of	O
this	O
distinction	O
is	O
,	O
e.g.	O
,	O
in	O
the	O
implementation	O
of	O
GUI	B-Application
applications	O
:	O
the	O
list	O
of	O
submenu	O
items	O
may	O
depend	O
on	O
the	O
state	O
of	O
the	O
application	O
;	O
this	O
list	O
may	O
be	O
updated	O
either	O
as	O
soon	O
as	O
the	O
state	O
of	O
the	O
application	O
changes	O
(	O
"	O
active	O
"	O
)	O
or	O
only	O
when	O
the	O
menu	O
is	O
invoked	O
(	O
"	O
passive	O
"	O
)	O
.	O
</s>
