<s>
A	O
keyspace	B-Application
(	O
or	O
key	B-Application
space	I-Application
)	O
in	O
a	O
NoSQL	B-General_Concept
data	B-General_Concept
store	I-General_Concept
is	O
an	O
object	O
that	O
holds	O
together	O
all	O
column	B-Application
families	I-Application
of	O
a	O
design	O
.	O
</s>
<s>
It	O
is	O
the	O
outermost	O
grouping	O
of	O
the	O
data	O
in	O
the	O
data	B-General_Concept
store	I-General_Concept
.	O
</s>
<s>
It	O
resembles	O
the	O
schema	B-Application
concept	O
in	O
Relational	B-Application
database	I-Application
management	I-Application
systems	I-Application
.	O
</s>
<s>
Generally	O
,	O
there	O
is	O
one	O
keyspace	B-Application
per	O
application	O
.	O
</s>
<s>
A	O
keyspace	B-Application
may	O
contain	O
column	B-Application
families	I-Application
or	O
super	B-General_Concept
columns	I-General_Concept
.	O
</s>
<s>
Each	O
super	B-General_Concept
column	I-General_Concept
contains	O
one	O
or	O
more	O
column	B-Application
families	I-Application
,	O
and	O
each	O
column	B-Application
family	I-Application
contains	O
at	O
least	O
one	O
column	O
.	O
</s>
<s>
The	O
keyspace	B-Application
is	O
the	O
highest	O
abstraction	O
in	O
a	O
distributed	O
data	B-General_Concept
store	I-General_Concept
.	O
</s>
<s>
The	O
keyspace	B-Application
has	O
similar	O
importance	O
like	O
a	O
schema	B-Application
has	O
in	O
a	O
database	O
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
schema	B-Application
,	O
however	O
,	O
it	O
does	O
not	O
stipulate	O
any	O
concrete	O
structure	O
,	O
like	O
it	O
is	O
known	O
in	O
the	O
entity-relationship	B-Architecture
model	I-Architecture
used	O
widely	O
in	O
the	O
relational	B-Architecture
data	I-Architecture
models	I-Architecture
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
contents	O
of	O
the	O
keyspace	B-Application
can	O
be	O
column	B-Application
families	I-Application
,	O
each	O
having	O
different	O
number	O
of	O
columns	O
,	O
or	O
even	O
different	O
columns	O
.	O
</s>
<s>
So	O
,	O
the	O
column	B-Application
families	I-Application
that	O
somehow	O
relate	O
to	O
the	O
row	B-Application
concept	O
in	O
relational	O
databases	O
do	O
not	O
stipulate	O
any	O
fixed	O
structure	O
.	O
</s>
<s>
The	O
only	O
point	O
that	O
is	O
the	O
same	O
with	O
a	O
schema	B-Application
is	O
that	O
it	O
also	O
contains	O
a	O
number	O
of	O
"	O
objects	O
"	O
,	O
which	O
are	O
tables	O
in	O
RDBMS	O
systems	O
and	O
here	O
column	B-Application
families	I-Application
or	O
super	B-General_Concept
columns	I-General_Concept
.	O
</s>
<s>
So	O
,	O
in	O
distributed	O
data	B-General_Concept
stores	I-General_Concept
,	O
the	O
whole	O
burden	O
to	O
handle	O
rows	O
that	O
may	O
even	O
change	O
from	O
data-store	O
update	O
to	O
update	O
lies	O
on	O
the	O
shoulders	O
of	O
the	O
programmers	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
we	O
show	O
a	O
number	O
of	O
column	B-Application
families	I-Application
in	O
a	O
keyspace	B-Application
.	O
</s>
<s>
Another	O
example	O
shows	O
a	O
simplified	O
Twitter	B-Application
clone	O
data	O
model	O
:	O
</s>
