<s>
A	O
natural	B-Application
key	I-Application
(	O
also	O
known	O
as	O
business	O
key	O
or	O
domain	B-Application
key	I-Application
)	O
is	O
a	O
type	O
of	O
unique	B-Application
key	I-Application
in	O
a	O
database	O
formed	O
of	O
attributes	O
that	O
exist	O
and	O
are	O
used	O
in	O
the	O
external	O
world	O
outside	O
the	O
database	O
(	O
i.e.	O
</s>
<s>
in	O
the	O
business	B-General_Concept
domain	I-General_Concept
or	O
domain	B-Algorithm
of	I-Algorithm
discourse	I-Algorithm
)	O
.	O
</s>
<s>
In	O
the	O
relational	B-Architecture
model	I-Architecture
of	O
data	O
,	O
a	O
natural	B-Application
key	I-Application
is	O
a	O
superkey	B-Application
and	O
is	O
therefore	O
a	O
functional	B-Application
determinant	I-Application
for	O
all	O
attributes	O
in	O
a	O
relation	O
.	O
</s>
<s>
A	O
natural	B-Application
key	I-Application
serves	O
two	O
complementary	O
purposes	O
:	O
</s>
<s>
The	O
uniqueness	B-Application
constraint	I-Application
assures	O
uniqueness	O
of	O
data	O
within	O
a	O
certain	O
technical	O
context	O
(	O
e.g.	O
</s>
<s>
This	O
means	O
that	O
the	O
user	O
can	O
rely	O
on	O
a	O
guaranteed	O
correspondence	O
between	O
facts	O
identified	O
by	O
key	O
values	O
recorded	O
in	O
a	O
system	O
and	O
the	O
external	O
domain	B-Algorithm
of	I-Algorithm
discourse	I-Algorithm
(	O
a	O
single	B-Application
version	I-Application
of	I-Application
the	I-Application
truth	I-Application
according	O
to	O
Kimball	O
)	O
.	O
</s>
<s>
A	O
natural	B-Application
key	I-Application
differs	O
from	O
a	O
surrogate	B-Application
key	I-Application
which	O
has	O
no	O
meaning	O
outside	O
the	O
database	O
itself	O
and	O
is	O
not	O
based	O
on	O
real-world	O
observation	O
or	O
intended	O
as	O
a	O
statement	O
about	O
the	O
reality	O
being	O
modelled	O
.	O
</s>
<s>
A	O
natural	B-Application
key	I-Application
therefore	O
provides	O
a	O
certain	O
data	O
quality	O
guarantee	O
whereas	O
a	O
surrogate	O
does	O
not	O
.	O
</s>
<s>
The	O
advantages	O
of	O
using	O
a	O
natural	B-Application
key	I-Application
to	O
uniquely	O
identify	O
records	O
in	O
a	O
relation	O
include	O
less	O
disk	O
space	O
usage	O
,	O
the	O
natural	B-Application
key	I-Application
is	O
an	O
attribute	O
that	O
is	O
related	O
to	O
the	O
business	O
or	O
the	O
real	O
world	O
so	O
in	O
most	O
cases	O
,	O
it	O
is	O
already	O
being	O
stored	O
in	O
the	O
relation	O
which	O
saves	O
disk	O
space	O
as	O
compared	O
to	O
creating	O
a	O
new	O
column	O
for	O
storing	O
the	O
surrogate	B-Application
key	I-Application
.	O
</s>
<s>
Another	O
advantage	O
of	O
using	O
natural	B-Application
keys	I-Application
is	O
that	O
it	O
simplifies	O
enforcement	O
of	O
data	O
quality	O
,	O
and	O
they	O
are	O
easier	O
to	O
relate	O
to	O
real	O
life	O
while	O
designing	O
the	O
database	O
system	O
.	O
</s>
<s>
They	O
simplify	O
the	O
quality	O
of	O
data	O
as	O
using	O
a	O
natural	B-Application
key	I-Application
that	O
is	O
unique	O
in	O
the	O
real	O
world	O
ensures	O
that	O
there	O
cannot	O
be	O
multiple	O
records	O
with	O
the	O
same	O
primary	B-Application
key	I-Application
.	O
</s>
<s>
Comparing	O
the	O
database	O
schema	O
to	O
a	O
real	O
world	O
scenario	O
is	O
a	O
huge	O
part	O
of	O
designing	O
a	O
database	O
schema	O
and	O
when	O
a	O
natural	B-Application
key	I-Application
is	O
being	O
used	O
in	O
the	O
tables	O
of	O
the	O
database	O
,	O
it	O
makes	O
it	O
easy	O
for	O
the	O
database	O
engineer	O
to	O
engineer	O
the	O
database	O
system	O
.	O
</s>
<s>
Usage	O
of	O
natural	B-Application
keys	I-Application
as	O
unique	O
identifiers	O
in	O
a	O
table	O
has	O
one	O
main	O
disadvantage	O
which	O
is	O
the	O
change	O
of	O
business	O
rules	O
or	O
the	O
change	O
of	O
rules	O
of	O
the	O
attribute	O
in	O
the	O
real	O
world	O
.	O
</s>
<s>
The	O
definition	O
of	O
the	O
structure	O
of	O
the	O
natural	B-Application
key	I-Application
attribute	O
might	O
change	O
in	O
the	O
future	O
.	O
</s>
<s>
For	O
example	O
if	O
there	O
is	O
a	O
table	O
storing	O
the	O
information	O
about	O
US	O
citizens	O
,	O
the	O
Social	O
Security	O
Number	O
would	O
act	O
as	O
the	O
natural	B-Application
key	I-Application
,	O
Social	O
Security	O
Number	O
being	O
the	O
natural	B-Application
key	I-Application
might	O
pose	O
a	O
problem	O
in	O
the	O
future	O
if	O
the	O
US	O
government	O
changes	O
the	O
structure	O
of	O
the	O
Social	O
Security	O
Number	O
and	O
increases	O
the	O
number	O
of	O
digits	O
in	O
the	O
SSN	O
due	O
to	O
some	O
reason	O
.	O
</s>
<s>
In	O
that	O
case	O
,	O
the	O
database	B-General_Concept
administrator	I-General_Concept
will	O
have	O
to	O
change	O
the	O
schema	O
of	O
the	O
table	O
and	O
perhaps	O
also	O
update	O
the	O
records	O
of	O
the	O
table	O
.	O
</s>
<s>
In	O
other	O
cases	O
,	O
this	O
can	O
prevent	O
improvements	O
of	O
the	O
system	O
altogether	O
due	O
to	O
too	O
extensive	O
effort	O
required	O
for	O
the	O
change	O
,	O
e.g.	O
,	O
the	O
inability	O
of	O
the	O
knowledge	O
management	O
software	O
Confluence	B-Protocol
,	O
to	O
represent	O
multiple	O
pages	O
with	O
the	O
same	O
title	O
.	O
</s>
