<s>
A	O
wide-column	B-Application
store	I-Application
(	O
or	O
extensible	O
record	O
store	O
)	O
is	O
a	O
column-oriented	B-General_Concept
DBMS	I-General_Concept
and	O
therefore	O
a	O
special	O
type	O
of	O
NoSQL	B-General_Concept
database	O
.	O
</s>
<s>
It	O
uses	O
tables	O
,	O
rows	O
,	O
and	O
columns	O
,	O
but	O
unlike	O
a	O
relational	B-Application
database	I-Application
,	O
the	O
names	O
and	O
format	O
of	O
the	O
columns	O
can	O
vary	O
from	O
row	O
to	O
row	O
in	O
the	O
same	O
table	O
.	O
</s>
<s>
A	O
wide-column	B-Application
store	I-Application
can	O
be	O
interpreted	O
as	O
a	O
two-dimensional	O
key	B-Data_Structure
–	I-Data_Structure
value	I-Data_Structure
store	I-Data_Structure
.	O
</s>
<s>
Wide-column	B-Application
stores	I-Application
such	O
as	O
Bigtable	B-Application
and	O
Apache	B-Application
Cassandra	I-Application
are	O
not	O
column	B-General_Concept
stores	I-General_Concept
in	O
the	O
original	O
sense	O
of	O
the	O
term	O
,	O
since	O
their	O
two-level	O
structures	O
do	O
not	O
use	O
a	O
columnar	O
data	O
layout	O
.	O
</s>
<s>
In	O
genuine	O
column	B-General_Concept
stores	I-General_Concept
,	O
a	O
columnar	O
data	O
layout	O
is	O
adopted	O
such	O
that	O
each	O
column	O
is	O
stored	O
separately	O
on	O
disk	O
.	O
</s>
<s>
Wide-column	B-Application
stores	I-Application
do	O
often	O
support	O
the	O
notion	O
of	O
column	B-Application
families	I-Application
that	O
are	O
stored	O
separately	O
.	O
</s>
<s>
However	O
,	O
each	O
such	O
column	B-Application
family	I-Application
typically	O
contains	O
multiple	O
columns	O
that	O
are	O
used	O
together	O
,	O
similar	O
to	O
traditional	O
relational	B-Application
database	I-Application
tables	O
.	O
</s>
<s>
Within	O
a	O
given	O
column	B-Application
family	I-Application
,	O
all	O
data	O
is	O
stored	O
in	O
a	O
row-by-row	O
fashion	O
,	O
such	O
that	O
the	O
columns	O
for	O
a	O
given	O
row	O
are	O
stored	O
together	O
,	O
rather	O
than	O
each	O
column	O
being	O
stored	O
separately	O
.	O
</s>
<s>
Wide-column	B-Application
stores	I-Application
that	O
support	O
column	B-Application
families	I-Application
are	O
also	O
known	O
as	O
column	B-Application
family	I-Application
databases	O
.	O
</s>
<s>
Google	B-Application
's	I-Application
Bigtable	B-Application
is	O
one	O
of	O
the	O
prototypical	O
examples	O
of	O
a	O
wide-column	B-Application
store	I-Application
.	O
</s>
<s>
Notable	O
wide-column	B-Application
stores	I-Application
include	O
:	O
</s>
