<s>
Apache	B-Application
CouchDB	I-Application
is	O
an	O
open-source	B-Application
document-oriented	B-General_Concept
NoSQL	B-General_Concept
database	O
,	O
implemented	O
in	O
Erlang	B-Operating_System
.	O
</s>
<s>
CouchDB	B-Application
uses	O
multiple	O
formats	O
and	O
protocols	O
to	O
store	O
,	O
transfer	O
,	O
and	O
process	O
its	O
data	O
.	O
</s>
<s>
It	O
uses	O
JSON	B-General_Concept
to	O
store	O
data	O
,	O
JavaScript	B-Language
as	O
its	O
query	O
language	O
using	O
MapReduce	B-Operating_System
,	O
and	O
HTTP	B-Protocol
for	O
an	O
API	B-General_Concept
.	O
</s>
<s>
CouchDB	B-Application
was	O
first	O
released	O
in	O
2005	O
and	O
later	O
became	O
an	O
Apache	O
Software	O
Foundation	O
project	O
in	O
2008	O
.	O
</s>
<s>
Unlike	O
a	O
relational	B-Application
database	I-Application
,	O
a	O
CouchDB	B-Application
database	O
does	O
not	O
store	O
data	O
and	O
relationships	O
in	O
tables	O
.	O
</s>
<s>
CouchDB	B-Application
implements	O
a	O
form	O
of	O
multiversion	B-Operating_System
concurrency	I-Operating_System
control	I-Operating_System
(	O
MVCC	O
)	O
so	O
it	O
does	O
not	O
lock	O
the	O
database	O
file	O
during	O
writes	O
.	O
</s>
<s>
Other	O
features	O
include	O
document-level	O
ACID	B-Operating_System
semantics	O
with	O
eventual	B-General_Concept
consistency	I-General_Concept
,	O
(	O
incremental	O
)	O
MapReduce	B-Operating_System
,	O
and	O
(	O
incremental	O
)	O
replication	O
.	O
</s>
<s>
One	O
of	O
CouchDB	B-Application
's	O
distinguishing	O
features	O
is	O
multi-master	B-Operating_System
replication	I-Operating_System
,	O
which	O
allows	O
it	O
to	O
scale	O
across	O
machines	O
to	O
build	O
high-performance	O
systems	O
.	O
</s>
<s>
The	O
CouchDB	B-Application
project	O
was	O
created	O
in	O
April	O
2005	O
by	O
Damien	O
Katz	O
,	O
a	O
former	O
Lotus	B-Operating_System
Notes	I-Operating_System
developer	O
at	O
IBM	O
.	O
</s>
<s>
He	O
self-funded	O
the	O
project	O
for	O
almost	O
two	O
years	O
and	O
released	O
it	O
as	O
an	O
open-source	B-Application
project	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
In	O
February	O
2008	O
,	O
it	O
became	O
an	O
Apache	B-Application
Incubator	I-Application
project	O
and	O
was	O
offered	O
under	O
the	O
Apache	B-Application
License	I-Application
instead	O
.	O
</s>
<s>
In	O
early	O
2012	O
,	O
Katz	O
left	O
the	O
project	O
to	O
focus	O
on	O
Couchbase	B-Operating_System
Server	I-Operating_System
.	O
</s>
<s>
Since	O
Katz	O
's	O
departure	O
,	O
the	O
Apache	B-Application
CouchDB	I-Application
project	O
has	O
continued	O
,	O
releasing	O
1.2	O
in	O
April	O
2012	O
and	O
1.3	O
in	O
April	O
2013	O
.	O
</s>
<s>
In	O
July	O
2013	O
,	O
the	O
CouchDB	B-Application
community	O
merged	O
the	O
codebase	O
for	O
BigCouch	B-General_Concept
,	O
Cloudant	B-General_Concept
's	O
clustered	O
version	O
of	O
CouchDB	B-Application
,	O
into	O
the	O
Apache	O
project	O
.	O
</s>
<s>
The	O
BigCouch	B-General_Concept
clustering	O
framework	O
is	O
included	O
in	O
the	O
current	O
release	O
of	O
Apache	B-Application
CouchDB	I-Application
.	O
</s>
<s>
And	O
the	O
new	O
Mango	O
Query	O
Server	O
provides	O
a	O
simple	O
JSON-based	O
way	O
to	O
perform	O
CouchDB	B-Application
queries	O
without	O
JavaScript	B-Language
or	O
MapReduce	B-Operating_System
.	O
</s>
<s>
CouchDB	B-Application
provides	O
ACID	B-Operating_System
semantics	O
.	O
</s>
<s>
It	O
does	O
this	O
by	O
implementing	O
a	O
form	O
of	O
Multi-Version	B-Operating_System
Concurrency	I-Operating_System
Control	I-Operating_System
,	O
meaning	O
that	O
CouchDB	B-Application
can	O
handle	O
a	O
high	O
volume	O
of	O
concurrent	B-Architecture
readers	O
and	O
writers	O
without	O
conflict	O
.	O
</s>
<s>
CouchDB	B-Application
can	O
replicate	O
to	O
devices	O
(	O
like	O
smartphones	O
)	O
that	O
can	O
go	O
offline	O
and	O
handle	O
data	O
sync	O
for	O
you	O
when	O
the	O
device	O
is	O
back	O
online	O
.	O
</s>
<s>
CouchDB	B-Application
was	O
designed	O
with	O
bi-directional	O
replication	O
(	O
or	O
synchronization	O
)	O
and	O
off-line	O
operation	O
in	O
mind	O
.	O
</s>
<s>
CouchDB	B-Application
stores	O
data	O
as	O
"	O
documents	O
"	O
,	O
as	O
one	O
or	O
more	O
field/value	O
pairs	O
expressed	O
as	O
JSON	B-General_Concept
.	O
</s>
<s>
Field	O
values	O
can	O
be	O
simple	O
things	O
like	O
strings	O
,	O
numbers	O
,	O
or	O
dates	O
;	O
but	O
ordered	B-Data_Structure
lists	I-Data_Structure
and	O
associative	B-Application
arrays	I-Application
can	O
also	O
be	O
used	O
.	O
</s>
<s>
Every	O
document	O
in	O
a	O
CouchDB	B-Application
database	O
has	O
a	O
unique	O
id	O
and	O
there	O
is	O
no	O
required	O
document	O
schema	O
.	O
</s>
<s>
CouchDB	B-Application
guarantees	O
eventual	B-General_Concept
consistency	I-General_Concept
to	O
be	O
able	O
to	O
provide	O
both	O
availability	O
and	O
partition	O
tolerance	O
.	O
</s>
<s>
In	O
CouchDB	B-Application
,	O
each	O
view	O
is	O
constructed	O
by	O
a	O
JavaScript	B-Language
function	O
that	O
acts	O
as	O
the	O
Map	O
half	O
of	O
a	O
map/reduce	B-Operating_System
operation	O
.	O
</s>
<s>
CouchDB	B-Application
can	O
index	O
views	O
and	O
keep	O
those	O
indexes	O
updated	O
as	O
documents	O
are	O
added	O
,	O
removed	O
,	O
or	O
updated	O
.	O
</s>
<s>
All	O
items	O
have	O
a	O
unique	O
URI	O
that	O
gets	O
exposed	O
via	O
HTTP	B-Protocol
.	I-Protocol
</s>
<s>
It	O
uses	O
the	O
HTTP	B-Protocol
methods	O
POST	O
,	O
GET	O
,	O
PUT	O
and	O
DELETE	O
for	O
the	O
four	O
basic	O
CRUD	B-General_Concept
(	O
Create	O
,	O
Read	O
,	O
Update	O
,	O
Delete	O
)	O
operations	O
on	O
all	O
resources	O
.	O
</s>
<s>
CouchDB	B-Application
also	O
offers	O
a	O
built-in	O
administration	O
interface	O
accessible	O
via	O
Web	O
called	O
Futon	O
.	O
</s>
<s>
Replication	O
and	O
synchronization	O
capabilities	O
of	O
CouchDB	B-Application
make	O
it	O
ideal	O
for	O
using	O
it	O
in	O
mobile	O
devices	O
,	O
where	O
network	O
connection	O
is	O
not	O
guaranteed	O
,	O
and	O
the	O
application	O
must	O
keep	O
on	O
working	O
offline	O
.	O
</s>
<s>
CouchDB	B-Application
is	O
well	O
suited	O
for	O
applications	O
with	O
accumulating	O
,	O
occasionally	O
changing	O
data	O
,	O
on	O
which	O
pre-defined	O
queries	O
are	O
to	O
be	O
run	O
and	O
where	O
versioning	O
is	O
important	O
(	O
CRM	O
,	O
CMS	O
systems	O
,	O
by	O
example	O
)	O
.	O
</s>
<s>
Users	O
of	O
CouchDB	B-Application
include	O
:	O
</s>
<s>
CERN	O
uses	O
CouchDB	B-Application
as	O
database	O
for	O
the	O
Data	O
Management	O
System	O
at	O
the	O
Large	O
Hadron	O
Collider	O
.	O
</s>
<s>
Here	O
CouchDB	B-Application
is	O
used	O
as	O
multi-node	O
peer-to-peer	O
offline-first	O
database	O
.	O
</s>
<s>
IBM	O
Cloud	O
services	O
are	O
based	O
at	O
a	O
fundamental	O
level	O
on	O
CouchDB	B-Application
.	O
</s>
<s>
United	O
Airlines	O
uses	O
CouchDB	B-Application
for	O
the	O
in-flight	O
entertainment	O
systems	O
in	O
over	O
3,000	O
planes	O
.	O
</s>
<s>
Meebo	B-Protocol
,	O
for	O
their	O
social	O
platform	O
(	O
Web	O
and	O
applications	O
)	O
.	O
</s>
<s>
Meebo	B-Protocol
was	O
acquired	O
by	O
Google	O
and	O
most	O
products	O
were	O
shut	O
down	O
on	O
July	O
12	O
,	O
2012	O
.	O
</s>
<s>
npm	B-Language
uses	O
CouchDB	B-Application
as	O
replicating	O
database	O
for	O
their	O
package	O
registry	O
.	O
</s>
<s>
CouchDB	B-Application
manages	O
a	O
collection	O
of	O
JSON	B-General_Concept
documents	O
.	O
</s>
<s>
Views	O
are	O
defined	O
with	O
aggregate	O
functions	O
and	O
filters	O
are	O
computed	O
in	O
parallel	O
,	O
much	O
like	O
MapReduce	B-Operating_System
.	O
</s>
<s>
CouchDB	B-Application
supports	O
a	O
view	O
system	O
using	O
external	O
socket	O
servers	O
and	O
a	O
JSON-based	O
protocol	O
.	O
</s>
<s>
As	O
a	O
consequence	O
,	O
view	O
servers	O
have	O
been	O
developed	O
in	O
a	O
variety	O
of	O
languages	O
(	O
JavaScript	B-Language
is	O
the	O
default	O
,	O
but	O
there	O
are	O
also	O
PHP	O
,	O
Ruby	O
,	O
Python	O
and	O
Erlang	B-Operating_System
)	O
.	O
</s>
<s>
Applications	O
interact	O
with	O
CouchDB	B-Application
via	O
HTTP	B-Protocol
.	I-Protocol
</s>
<s>
The	O
following	O
demonstrates	O
a	O
few	O
examples	O
using	O
cURL	B-Language
,	O
a	O
command-line	O
utility	O
.	O
</s>
<s>
These	O
examples	O
assume	O
that	O
CouchDB	B-Application
is	O
running	O
on	O
localhost	B-Protocol
(	O
127.0.0.1	B-Protocol
)	O
on	O
port	O
5984	O
.	O
</s>
<s>
"	O
couchdb	B-Application
"	O
:	O
"	O
Welcome	O
"	O
,	O
</s>
<s>
CouchDB	B-Application
includes	O
a	O
number	O
of	O
other	O
open	O
source	O
projects	O
as	O
part	O
of	O
its	O
default	O
package	O
.	O
</s>
<s>
Component	O
Description	O
License	O
Erlang	B-Operating_System
Erlang	B-Operating_System
is	O
a	O
general-purpose	O
concurrent	B-Architecture
programming	I-Architecture
language	O
and	O
runtime	B-Device
system	I-Device
.	O
</s>
<s>
The	O
sequential	O
subset	O
of	O
Erlang	B-Operating_System
is	O
a	O
functional	B-Language
language	I-Language
with	O
strict	O
evaluation	O
,	O
single	O
assignment	O
,	O
and	O
dynamic	O
typing	O
Apache	B-Application
2.0	I-Application
(	O
Release	O
18.0	O
and	O
later	O
)	O
Erlang	B-General_Concept
Public	I-General_Concept
License	I-General_Concept
(	O
Earlier	O
releases	O
)	O
ICU	B-Application
International	B-Application
Components	I-Application
for	I-Application
Unicode	I-Application
(	O
ICU	B-Application
)	O
is	O
an	O
open-source	B-Application
project	O
of	O
mature	O
C/C	O
++	O
and	O
Java	B-Language
libraries	O
for	O
Unicode	O
support	O
,	O
software	O
internationalization	O
and	O
software	O
globalization	O
Unicode	O
License	O
jQuery	B-Language
jQuery	B-Language
is	O
a	O
lightweight	O
cross-browser	B-Architecture
JavaScript	B-Language
library	I-Language
that	O
emphasizes	O
interaction	O
between	O
JavaScript	B-Language
and	O
HTML	B-Language
MIT	B-License
License	I-License
OpenSSL	B-Language
OpenSSL	B-Language
is	O
an	O
open-source	B-Application
implementation	O
of	O
the	O
SSL	B-Protocol
and	I-Protocol
TLS	I-Protocol
protocols	O
.	O
</s>
<s>
The	O
core	O
library	B-Library
(	O
written	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
)	O
implements	O
the	O
basic	O
cryptographic	O
functions	O
and	O
provides	O
various	O
utility	O
functions	O
Apache	B-Application
1.0	I-Application
and	O
the	O
four-clause	O
BSD	O
License	O
SpiderMonkey	B-Language
SpiderMonkey	B-Language
is	O
a	O
performant	O
JavaScript	B-Language
engine	I-Language
maintained	O
by	O
the	B-Operating_System
Mozilla	I-Operating_System
Foundation	I-Operating_System
.	O
</s>
