<s>
Database	B-General_Concept
virtualization	I-General_Concept
is	O
the	O
decoupling	O
of	O
the	O
database	O
layer	O
,	O
which	O
lies	O
between	O
the	O
storage	O
and	O
application	O
layers	O
within	O
the	O
application	O
stack	O
.	O
</s>
<s>
In	O
both	O
cases	O
,	O
database	B-General_Concept
virtualization	I-General_Concept
provides	O
increased	O
flexibility	O
,	O
more	O
granular	O
and	O
efficient	O
allocation	O
of	O
pooled	O
resources	O
,	O
and	O
more	O
scalable	O
computing	O
.	O
</s>
<s>
There	O
are	O
two	O
primary	O
ways	O
that	O
data	O
has	O
been	O
partitioned	O
inside	O
legacy	O
data	B-General_Concept
management	I-General_Concept
systems	O
:	O
</s>
<s>
Shared-data	O
data	B-General_Concept
management	I-General_Concept
systems	O
are	O
limited	O
to	O
single-digit	O
node	O
clusters	O
.	O
</s>
<s>
“	O
Shared-data	O
”	O
and	O
“	O
shared-nothing	O
”	O
architectures	O
allow	O
scalability	O
through	O
multiple	O
data	O
partitions	O
and	O
cross-partition	O
querying	O
and	O
transaction	B-General_Concept
processing	I-General_Concept
without	O
full	O
partition	O
scanning	O
.	O
</s>
<s>
With	O
greater	O
numbers	O
of	O
database	O
sources	O
,	O
inserting	O
a	O
horizontal	O
data	B-General_Concept
virtualization	I-General_Concept
layer	O
between	O
the	O
sources	O
and	O
consumers	O
helps	O
address	O
this	O
complexity	O
.	O
</s>
<s>
Rick	O
van	O
der	O
Lans	O
,	O
the	O
author	O
of	O
multiple	O
books	O
on	O
SQL	O
and	O
relational	O
databases	O
,	O
has	O
defined	O
data	B-General_Concept
virtualization	I-General_Concept
as	O
"	O
the	O
process	O
of	O
offering	O
data	O
consumers	O
a	O
data	O
access	O
interface	O
that	O
hides	O
the	O
technical	O
aspects	O
of	O
stored	O
data	O
,	O
such	O
as	O
location	O
,	O
storage	O
structure	O
,	O
API	O
,	O
access	O
language	O
,	O
and	O
storage	O
technology.	O
"	O
</s>
<s>
Increased	O
fault	B-General_Concept
tolerance	I-General_Concept
.	O
</s>
