<s>
In	O
object-oriented	B-Language
programming	I-Language
,	O
association	O
defines	O
a	O
relationship	O
between	O
classes	O
of	O
objects	O
that	O
allows	O
one	O
object	O
instance	O
to	O
cause	O
another	O
to	O
perform	O
an	O
action	O
on	O
its	O
behalf	O
.	O
</s>
<s>
In	O
generic	O
terms	O
,	O
the	O
causation	B-Application
is	O
usually	O
called	O
"	O
sending	O
a	O
message	O
"	O
,	O
"	O
invoking	O
a	O
method	B-Language
"	O
or	O
"	O
calling	O
a	O
member	O
function	O
"	O
to	O
the	O
controlled	O
object	O
.	O
</s>
<s>
Concrete	O
implementation	O
usually	O
requires	O
the	O
requesting	O
object	O
to	O
invoke	O
a	O
method	B-Language
or	O
member	O
function	O
using	O
a	O
reference	O
or	O
pointer	O
to	O
the	O
memory	O
location	O
of	O
the	O
controlled	O
object	O
.	O
</s>
<s>
The	O
objects	O
that	O
are	O
related	O
via	O
the	O
association	O
are	O
considered	O
to	O
act	O
in	O
a	O
role	B-General_Concept
with	O
respect	O
to	O
the	O
association	O
,	O
if	O
object	O
's	O
current	O
state	O
in	O
the	O
active	O
situation	O
allows	O
the	O
other	O
associated	O
objects	O
to	O
use	O
the	O
object	O
in	O
the	O
manner	O
specified	O
by	O
the	O
role	B-General_Concept
.	O
</s>
<s>
A	O
role	B-General_Concept
can	O
be	O
used	O
to	O
distinguish	O
two	O
objects	O
of	O
the	O
same	O
class	O
when	O
describing	O
its	O
use	O
in	O
the	O
context	O
of	O
the	O
association	O
.	O
</s>
<s>
A	O
role	B-General_Concept
describes	O
the	O
public	O
aspects	O
of	O
an	O
object	O
with	O
respect	O
to	O
an	O
association	O
.	O
</s>
