<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
a	O
multimap	B-Language
(	O
sometimes	O
also	O
multihash	B-Application
,	O
multidict	B-Application
or	O
multidictionary	B-Application
)	O
is	O
a	O
generalization	O
of	O
a	O
map	B-Application
or	I-Application
associative	I-Application
array	I-Application
abstract	O
data	O
type	O
in	O
which	O
more	O
than	O
one	O
value	O
may	O
be	O
associated	O
with	O
and	O
returned	O
for	O
a	O
given	O
key	O
.	O
</s>
<s>
Both	O
map	O
and	O
multimap	B-Language
are	O
particular	O
cases	O
of	O
containers	B-Application
(	O
for	O
example	O
,	O
see	O
C++	B-Language
Standard	B-Application
Template	I-Application
Library	I-Application
containers	B-Application
)	O
.	O
</s>
<s>
Often	O
the	O
multimap	B-Language
is	O
implemented	O
as	O
a	O
map	O
with	O
lists	O
or	O
sets	O
as	O
the	O
map	O
values	O
.	O
</s>
<s>
The	O
index	O
of	O
a	O
book	O
may	O
report	O
any	O
number	O
of	O
references	O
for	O
a	O
given	O
index	O
term	O
,	O
and	O
thus	O
may	O
be	O
coded	O
as	O
a	O
multimap	B-Language
from	O
index	O
terms	O
to	O
any	O
number	O
of	O
reference	O
locations	O
or	O
pages	O
.	O
</s>
<s>
Querystrings	B-Protocol
may	O
have	O
multiple	O
values	O
associated	O
with	O
a	O
single	O
field	O
.	O
</s>
<s>
This	O
is	O
commonly	O
generated	O
when	O
a	O
web	B-General_Concept
form	I-General_Concept
allows	O
multiple	O
check	O
boxes	O
or	O
selections	O
to	O
be	O
chosen	O
in	O
response	O
to	O
a	O
single	O
form	O
element	O
.	O
</s>
<s>
C++'s	O
Standard	B-Application
Template	I-Application
Library	I-Application
provides	O
the	O
multimap	B-Language
container	B-Application
for	O
the	O
sorted	O
multimap	B-Language
using	O
a	O
self-balancing	B-Data_Structure
binary	I-Data_Structure
search	I-Data_Structure
tree	I-Data_Structure
,	O
and	O
SGI	O
's	O
STL	O
extension	O
provides	O
the	O
hash_multimap	O
container	B-Application
,	O
which	O
implements	O
a	O
multimap	B-Language
using	O
a	O
hash	B-Algorithm
table	I-Algorithm
.	O
</s>
<s>
As	O
of	O
C++11	O
,	O
the	O
Standard	B-Application
Template	I-Application
Library	I-Application
provides	O
the	O
unordered_multimap	O
for	O
the	O
unordered	O
multimap	B-Language
.	O
</s>
<s>
Quiver	O
provides	O
a	O
Multimap	B-Language
for	O
Dart	B-Language
.	O
</s>
<s>
Apache	B-Language
Commons	I-Language
Collections	O
provides	O
a	O
MultiMap	B-Language
interface	O
for	O
Java	B-Language
.	O
</s>
<s>
It	O
also	O
provides	O
a	O
MultiValueMap	O
implementing	O
class	O
that	O
makes	O
a	O
MultiMap	B-Language
out	O
of	O
a	O
Map	O
object	O
and	O
a	O
type	O
of	O
Collection	O
.	O
</s>
<s>
Google	B-Language
Guava	I-Language
provides	O
a	O
Multimap	B-Language
interface	O
and	O
implementations	O
of	O
it	O
.	O
</s>
<s>
Python	O
provides	O
a	O
collections.defaultdict	O
class	O
that	O
can	O
be	O
used	O
to	O
create	O
a	O
multimap	B-Language
.	O
</s>
<s>
OCaml	B-Language
's	O
standard	O
library	O
module	O
Hashtbl	O
implements	O
a	O
hash	B-Algorithm
table	I-Algorithm
where	O
it	O
's	O
possible	O
to	O
store	O
multiple	O
values	O
for	O
a	O
key	O
.	O
</s>
<s>
The	O
Scala	B-Application
programming	I-Application
language	I-Application
's	O
API	O
also	O
provides	O
Multimap	B-Language
and	O
implementations	O
.	O
</s>
