<s>
In	O
systems	O
analysis	O
,	O
a	O
many-to-many	B-Application
relationship	O
is	O
a	O
type	O
of	O
cardinality	B-Application
that	O
refers	O
to	O
the	O
relationship	O
between	O
two	O
entities	O
,	O
say	O
,	O
A	O
and	O
B	O
,	O
where	O
A	O
may	O
contain	O
a	O
parent	O
instance	O
for	O
which	O
there	O
are	O
many	O
children	O
in	O
B	O
and	O
vice	O
versa	O
.	O
</s>
<s>
In	O
a	O
relational	O
database	O
management	O
system	O
,	O
such	O
relationships	O
are	O
usually	O
implemented	O
by	O
means	O
of	O
an	O
associative	B-Application
table	I-Application
(	O
also	O
known	O
as	O
join	B-Application
table	I-Application
,	O
junction	B-Application
table	I-Application
or	O
cross-reference	B-Application
table	I-Application
)	O
,	O
say	O
,	O
AB	O
with	O
two	O
one-to-many	B-Application
relationships	O
and	O
.	O
</s>
<s>
In	O
this	O
case	O
the	O
logical	O
primary	B-Application
key	I-Application
for	O
AB	O
is	O
formed	O
from	O
the	O
two	O
foreign	B-Application
keys	I-Application
(	O
i.e.	O
</s>
<s>
copies	O
of	O
the	O
primary	B-Application
keys	I-Application
of	O
A	O
and	O
B	O
)	O
.	O
</s>
<s>
In	O
web	B-Application
application	I-Application
frameworks	I-Application
such	O
as	O
CakePHP	B-Language
and	O
Ruby	B-Application
on	I-Application
Rails	I-Application
,	O
a	O
many-to-many	B-Application
relationship	O
between	O
entity	O
types	O
represented	O
by	O
logical	O
model	O
database	O
tables	O
is	O
sometimes	O
referred	O
to	O
as	O
a	O
HasAndBelongsToMany	O
(	O
HABTM	B-Application
)	O
relationship	O
.	O
</s>
