<s>
A	O
column	O
of	O
a	O
distributed	O
data	O
store	O
is	O
a	O
NoSQL	B-General_Concept
object	O
of	O
the	O
lowest	O
level	O
in	O
a	O
keyspace	B-Application
.	O
</s>
<s>
It	O
is	O
a	O
tuple	B-Application
(	O
a	O
key	B-Application
–	I-Application
value	I-Application
pair	I-Application
)	O
consisting	O
of	O
three	O
elements	O
:	O
</s>
<s>
According	O
to	O
the	O
CAP	B-Operating_System
theorem	I-Operating_System
,	O
distributed	O
data	O
stores	O
cannot	O
guarantee	O
consistency	B-General_Concept
,	O
as	O
availability	O
and	O
partition	B-Algorithm
tolerance	I-Algorithm
are	O
more	O
important	O
issues	O
.	O
</s>
<s>
Some	O
data	O
stores	O
,	O
like	O
Riak	B-General_Concept
,	O
may	O
use	O
the	O
more	O
sophisticated	O
vector	B-Operating_System
clock	I-Operating_System
instead	O
of	O
the	O
timestamp	O
to	O
resolve	O
stale	O
information	O
.	O
</s>
<s>
In	O
relational	B-Application
databases	I-Application
,	O
a	O
column	O
is	O
a	O
part	O
of	O
a	O
relational	O
table	O
that	O
can	O
be	O
seen	O
in	O
each	O
row	O
of	O
the	O
table	O
.	O
</s>
<s>
A	O
column	O
can	O
be	O
part	O
of	O
a	O
ColumnFamily	B-Application
that	O
resembles	O
at	O
most	O
a	O
relational	O
row	O
,	O
but	O
it	O
may	O
appear	O
in	O
one	O
row	O
and	O
not	O
in	O
the	O
others	O
.	O
</s>
<s>
Three	O
definitions	O
of	O
columns	O
in	O
JSON-like	B-General_Concept
notation	O
are	O
given	O
below	O
:	O
</s>
