<s>
Database	B-Application
normalization	I-Application
or	O
database	B-Application
normalisation	I-Application
(	O
see	O
spelling	O
differences	O
)	O
is	O
the	O
process	O
of	O
structuring	O
a	O
relational	B-Application
database	I-Application
in	O
accordance	O
with	O
a	O
series	O
of	O
so-called	O
normal	B-Application
forms	I-Application
in	O
order	O
to	O
reduce	O
data	B-Application
redundancy	I-Application
and	O
improve	O
data	O
integrity	O
.	O
</s>
<s>
It	O
was	O
first	O
proposed	O
by	O
British	O
computer	O
scientist	O
Edgar	O
F	O
.	O
Codd	O
as	O
part	O
of	O
his	O
relational	B-Architecture
model	I-Architecture
.	O
</s>
<s>
Normalization	B-Application
entails	O
organizing	O
the	O
columns	B-Application
(	O
attributes	O
)	O
and	O
tables	B-Language
(	O
relations	O
)	O
of	O
a	O
database	O
to	O
ensure	O
that	O
their	O
dependencies	O
are	O
properly	O
enforced	O
by	O
database	O
integrity	O
constraints	O
.	O
</s>
<s>
A	O
basic	O
objective	O
of	O
the	O
first	O
normal	B-Application
form	I-Application
defined	O
by	O
Codd	O
in	O
1970	O
was	O
to	O
permit	O
data	O
to	O
be	O
queried	O
and	O
manipulated	O
using	O
a	O
"	O
universal	O
data	O
sub-language	O
"	O
grounded	O
in	O
first-order	O
logic	O
.	O
</s>
<s>
An	O
example	O
of	O
such	O
a	O
language	O
is	O
SQL	B-Language
,	O
though	O
it	O
is	O
one	O
that	O
Codd	O
regarded	O
as	O
seriously	O
flawed	O
.	O
</s>
<s>
The	O
objectives	O
of	O
normalisation	O
beyond	O
1NF	O
(	O
first	O
normal	B-Application
form	I-Application
)	O
were	O
stated	O
by	O
Codd	O
as	O
:	O
</s>
<s>
Insertion	B-Application
anomaly	I-Application
.	O
</s>
<s>
Therefore	O
,	O
the	O
details	O
of	O
any	O
faculty	O
member	O
who	O
teaches	O
at	O
least	O
one	O
course	O
can	O
be	O
recorded	O
,	O
but	O
a	O
newly	O
hired	O
faculty	O
member	O
who	O
has	O
not	O
yet	O
been	O
assigned	O
to	O
teach	O
any	O
courses	O
cannot	O
be	O
recorded	O
,	O
except	O
by	O
setting	O
the	O
Course	O
Code	O
to	O
null	B-Language
.	O
</s>
<s>
Update	B-Application
anomaly	I-Application
.	O
</s>
<s>
Deletion	B-Application
anomaly	I-Application
.	O
</s>
<s>
The	O
"	O
Faculty	O
and	O
Their	O
Courses	O
"	O
relation	O
described	O
in	O
the	O
previous	O
example	O
suffers	O
from	O
this	O
type	O
of	O
anomaly	O
,	O
for	O
if	O
a	O
faculty	O
member	O
temporarily	O
ceases	O
to	O
be	O
assigned	O
to	O
any	O
courses	O
,	O
the	O
last	O
of	O
the	O
records	O
on	O
which	O
that	O
faculty	O
member	O
appears	O
must	O
be	O
deleted	O
,	O
effectively	O
also	O
deleting	O
the	O
faculty	O
member	O
,	O
unless	O
the	O
Course	O
Code	O
field	O
is	O
set	O
to	O
null	B-Language
.	O
</s>
<s>
Codd	O
introduced	O
the	O
concept	O
of	O
normalization	B-Application
and	O
what	O
is	O
now	O
known	O
as	O
the	O
first	O
normal	B-Application
form	I-Application
(	O
1NF	O
)	O
in	O
1970	O
.	O
</s>
<s>
Codd	O
went	O
on	O
to	O
define	O
the	O
second	O
normal	B-Application
form	I-Application
(	O
2NF	O
)	O
and	O
third	O
normal	B-Application
form	I-Application
(	O
3NF	O
)	O
in	O
1971	O
,	O
and	O
Codd	O
and	O
Raymond	O
F	O
.	O
Boyce	O
defined	O
the	O
Boyce	O
–	O
Codd	O
normal	B-Application
form	I-Application
(	O
BCNF	O
)	O
in	O
1974	O
.	O
</s>
<s>
Informally	O
,	O
a	O
relational	B-Application
database	I-Application
relation	O
is	O
often	O
described	O
as	O
"	O
normalized	O
"	O
if	O
it	O
meets	O
third	O
normal	B-Application
form	I-Application
.	O
</s>
<s>
Most	O
3NF	O
relations	O
are	O
free	O
of	O
insertion	O
,	O
updation	O
,	O
and	O
deletion	B-Application
anomalies	I-Application
.	O
</s>
<s>
The	O
normal	B-Application
forms	I-Application
(	O
from	O
least	O
normalized	O
to	O
most	O
normalized	O
)	O
are	O
:	O
</s>
<s>
Normalization	B-Application
is	O
a	O
database	O
design	O
technique	O
,	O
which	O
is	O
used	O
to	O
design	O
a	O
relational	B-Application
database	I-Application
table	O
up	O
to	O
higher	O
normal	B-Application
form	I-Application
.	O
</s>
<s>
The	O
process	O
is	O
progressive	O
,	O
and	O
a	O
higher	O
level	O
of	O
database	B-Application
normalization	I-Application
cannot	O
be	O
achieved	O
unless	O
the	O
previous	O
levels	O
have	O
been	O
satisfied	O
.	O
</s>
<s>
That	O
means	O
that	O
,	O
having	O
data	O
in	O
unnormalized	B-Application
form	I-Application
(	O
the	O
least	O
normalized	O
)	O
and	O
aiming	O
to	O
achieve	O
the	O
highest	O
level	O
of	O
normalization	B-Application
,	O
the	O
first	O
step	O
would	O
be	O
to	O
ensure	O
compliance	O
to	O
first	O
normal	B-Application
form	I-Application
,	O
the	O
second	O
step	O
would	O
be	O
to	O
ensure	O
second	O
normal	B-Application
form	I-Application
is	O
satisfied	O
,	O
and	O
so	O
forth	O
in	O
order	O
mentioned	O
above	O
,	O
until	O
the	O
data	O
conform	O
to	O
sixth	O
normal	B-Application
form	I-Application
.	O
</s>
<s>
However	O
,	O
it	O
is	O
worth	O
noting	O
that	O
normal	B-Application
forms	I-Application
beyond	O
4NF	O
are	O
mainly	O
of	O
academic	O
interest	O
,	O
as	O
the	O
problems	O
they	O
exist	O
to	O
solve	O
rarely	O
appear	O
in	O
practice	O
.	O
</s>
<s>
The	O
data	O
in	O
the	O
following	O
example	O
were	O
intentionally	O
designed	O
to	O
contradict	O
most	O
of	O
the	O
normal	B-Application
forms	I-Application
.	O
</s>
<s>
In	O
real	O
life	O
,	O
it	O
is	O
quite	O
possible	O
to	O
be	O
able	O
to	O
skip	O
some	O
of	O
the	O
normalization	B-Application
steps	O
because	O
the	O
table	O
does	O
n't	O
contain	O
anything	O
contradicting	O
the	O
given	O
normal	B-Application
form	I-Application
.	O
</s>
<s>
It	O
also	O
commonly	O
occurs	O
that	O
fixing	O
a	O
violation	O
of	O
one	O
normal	B-Application
form	I-Application
also	O
fixes	O
a	O
violation	O
of	O
a	O
higher	O
normal	B-Application
form	I-Application
in	O
the	O
process	O
.	O
</s>
<s>
Also	O
one	O
table	O
has	O
been	O
chosen	O
for	O
normalization	B-Application
at	O
each	O
step	O
,	O
meaning	O
that	O
at	O
the	O
end	O
of	O
this	O
example	O
process	O
,	O
there	O
might	O
still	O
be	O
some	O
tables	B-Language
not	O
satisfying	O
the	O
highest	O
normal	B-Application
form	I-Application
.	O
</s>
<s>
As	O
a	O
prerequisite	O
to	O
conform	O
to	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
a	O
table	O
must	O
have	O
a	O
primary	B-Application
key	I-Application
,	O
which	O
uniquely	O
identifies	O
a	O
row	O
.	O
</s>
<s>
Two	O
books	O
could	O
have	O
the	O
same	O
title	O
,	O
but	O
an	O
ISBN	O
uniquely	O
identifies	O
a	O
book	O
,	O
so	O
it	O
can	O
be	O
used	O
as	O
the	O
primary	B-Application
key	I-Application
:	O
</s>
<s>
To	O
satisfy	O
First	O
normal	B-Application
form	I-Application
,	O
each	O
column	O
of	O
a	O
table	O
must	O
have	O
a	O
single	O
value	O
.	O
</s>
<s>
Columns	B-Application
which	O
contain	O
sets	O
of	O
values	O
or	O
nested	O
records	O
are	O
not	O
allowed	O
.	O
</s>
<s>
A	O
foreign	O
key	O
column	O
is	O
added	O
to	O
the	O
Subject-table	O
,	O
which	O
refers	O
to	O
the	O
primary	B-Application
key	I-Application
of	O
the	O
row	O
from	O
which	O
the	O
subject	O
was	O
extracted	O
.	O
</s>
<s>
Instead	O
of	O
one	O
table	O
in	O
unnormalized	B-Application
form	I-Application
,	O
there	O
are	O
now	O
two	O
tables	B-Language
conforming	O
to	O
the	O
1NF	O
.	O
</s>
<s>
If	O
a	O
table	O
has	O
a	O
single	O
column	O
primary	B-Application
key	I-Application
,	O
it	O
automatically	O
satisfies	O
2NF	O
,	O
but	O
if	O
a	O
table	O
has	O
a	O
multi-column	O
or	O
composite	B-Application
key	I-Application
then	O
it	O
may	O
not	O
satisfy	O
2NF	O
.	O
</s>
<s>
The	O
Book	O
table	O
below	O
has	O
a	O
composite	B-Application
key	I-Application
of	O
{	O
Title	O
,	O
Format}	O
(	O
indicated	O
by	O
the	O
underlining	O
)	O
,	O
so	O
it	O
may	O
not	O
satisfy	O
2NF	O
.	O
</s>
<s>
At	O
this	O
point	O
in	O
our	O
design	O
the	O
key	O
is	O
not	O
finalised	O
as	O
the	O
primary	B-Application
key	I-Application
,	O
so	O
it	O
is	O
called	O
a	O
candidate	B-Application
key	I-Application
.	O
</s>
<s>
All	O
of	O
the	O
attributes	O
that	O
are	O
not	O
part	O
of	O
the	O
candidate	B-Application
key	I-Application
depend	O
on	O
Title	O
,	O
but	O
only	O
Price	O
also	O
depends	O
on	O
Format	O
.	O
</s>
<s>
To	O
conform	O
to	O
2NF	O
and	O
remove	O
duplicities	O
,	O
every	O
non-candidate-key	O
attribute	O
must	O
depend	O
on	O
the	O
whole	O
candidate	B-Application
key	I-Application
,	O
not	O
just	O
part	O
of	O
it	O
.	O
</s>
<s>
To	O
normalize	O
this	O
table	O
,	O
make	O
 { Title } 	O
a	O
(	O
simple	O
)	O
candidate	B-Application
key	I-Application
(	O
the	O
primary	B-Application
key	I-Application
)	O
so	O
that	O
every	O
non-candidate-key	O
attribute	O
depends	O
on	O
the	O
whole	O
candidate	B-Application
key	I-Application
,	O
and	O
remove	O
Price	O
into	O
a	O
separate	O
table	O
so	O
that	O
its	O
dependency	O
on	O
Format	O
can	O
be	O
preserved	O
:	O
</s>
<s>
The	O
Book	O
table	O
still	O
has	O
a	O
transitive	O
functional	B-Application
dependency	I-Application
( {	O
Author	O
Nationality}	O
is	O
dependent	O
on	O
{Author},	O
which	O
is	O
dependent	O
on	O
 { Title } 	O
)	O
.	O
</s>
<s>
To	O
make	O
it	O
in	O
3NF	O
,	O
let	O
's	O
use	O
the	O
following	O
table	O
structure	O
,	O
thereby	O
eliminating	O
the	O
transitive	O
functional	B-Application
dependencies	I-Application
by	O
placing	O
{	O
Author	O
Nationality}	O
and	O
{	O
Genre	O
Name}	O
in	O
their	O
own	O
respective	O
tables	B-Language
:	O
</s>
<s>
The	O
elementary	O
key	O
normal	B-Application
form	I-Application
(	O
EKNF	O
)	O
falls	O
strictly	O
between	O
3NF	O
and	O
BCNF	O
and	O
is	O
not	O
much	O
discussed	O
in	O
the	O
literature	O
.	O
</s>
<s>
As	O
this	O
table	O
structure	O
consists	O
of	O
a	O
compound	B-Application
primary	I-Application
key	I-Application
,	O
it	O
does	O
n't	O
contain	O
any	O
non-key	O
attributes	O
and	O
it	O
's	O
already	O
in	O
BCNF	O
(	O
and	O
therefore	O
also	O
satisfies	O
all	O
the	O
previous	O
normal	B-Application
forms	I-Application
)	O
.	O
</s>
<s>
That	O
means	O
that	O
,	O
to	O
satisfy	O
the	O
fourth	O
normal	B-Application
form	I-Application
,	O
this	O
table	O
needs	O
to	O
be	O
decomposed	O
as	O
well	O
:	O
</s>
<s>
Now	O
,	O
every	O
record	O
is	O
unambiguously	O
identified	O
by	O
a	O
superkey	B-Application
,	O
therefore	O
4NF	O
is	O
satisfied	O
.	O
</s>
<s>
No	O
component	O
of	O
that	O
join	O
dependency	O
is	O
a	O
superkey	B-Application
(	O
the	O
sole	O
superkey	B-Application
being	O
the	O
entire	O
heading	O
)	O
,	O
so	O
the	O
table	O
does	O
not	O
satisfy	O
the	O
ETNF	O
and	O
can	O
be	O
further	O
decomposed	O
:	O
</s>
<s>
Decomposing	O
this	O
table	O
lowers	O
redundancies	B-Application
,	O
resulting	O
in	O
the	O
following	O
two	O
tables	B-Language
:	O
</s>
<s>
The	O
query	O
joining	O
these	O
tables	B-Language
would	O
return	O
the	O
following	O
data	O
:	O
</s>
<s>
The	O
JOIN	O
returns	O
three	O
more	O
rows	O
than	O
it	O
should	O
;	O
adding	O
another	O
table	O
to	O
clarify	O
the	O
relation	O
results	O
in	O
three	O
separate	O
tables	B-Language
:	O
</s>
<s>
It	O
actually	O
is	O
not	O
possible	O
to	O
join	O
these	O
three	O
tables	B-Language
.	O
</s>
<s>
Let	O
's	O
have	O
a	O
look	O
at	O
the	O
Book	O
table	O
from	O
previous	O
examples	O
and	O
see	O
if	O
it	O
satisfies	O
the	O
Domain-key	O
normal	B-Application
form	I-Application
:	O
</s>
<s>
A	O
simple	O
and	O
intuitive	O
definition	O
of	O
the	O
sixth	O
normal	B-Application
form	I-Application
is	O
that	O
"	O
a	O
table	O
is	O
in	O
6NF	O
when	O
the	O
row	O
contains	O
the	O
Primary	B-Application
Key	I-Application
,	O
and	O
at	O
most	O
one	O
other	O
attribute	O
"	O
.	O
</s>
<s>
needs	O
to	O
be	O
further	O
decomposed	O
into	O
two	O
tables	B-Language
:	O
</s>
<s>
The	O
obvious	O
drawback	O
of	O
6NF	O
is	O
the	O
proliferation	O
of	O
tables	B-Language
required	O
to	O
represent	O
the	O
information	O
on	O
a	O
single	O
entity	O
.	O
</s>
<s>
If	O
a	O
table	O
in	O
5NF	O
has	O
one	O
primary	B-Application
key	I-Application
column	O
and	O
N	O
attributes	O
,	O
representing	O
the	O
same	O
information	O
in	O
6NF	O
will	O
require	O
N	O
tables	B-Language
;	O
multi-field	O
updates	O
to	O
a	O
single	O
conceptual	O
record	O
will	O
require	O
updates	O
to	O
multiple	O
tables	B-Language
;	O
and	O
inserts	O
and	O
deletes	O
will	O
similarly	O
require	O
operations	O
across	O
multiple	O
tables	B-Language
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
in	O
databases	O
intended	O
to	O
serve	O
Online	B-General_Concept
Transaction	I-General_Concept
Processing	I-General_Concept
needs	O
,	O
6NF	O
should	O
not	O
be	O
used	O
.	O
</s>
<s>
However	O
,	O
in	O
data	O
warehouses	O
,	O
which	O
do	O
not	O
permit	O
interactive	O
updates	O
and	O
which	O
are	O
specialized	O
for	O
fast	O
query	O
on	O
large	O
data	O
volumes	O
,	O
certain	O
DBMSs	O
use	O
an	O
internal	O
6NF	O
representation	O
–	O
known	O
as	O
a	O
columnar	B-General_Concept
data	I-General_Concept
store	I-General_Concept
.	O
</s>
<s>
In	O
all	O
these	O
cases	O
,	O
however	O
,	O
the	O
database	O
designer	O
does	O
not	O
have	O
to	O
perform	O
6NF	O
normalization	B-Application
manually	O
by	O
creating	O
separate	O
tables	B-Language
.	O
</s>
<s>
Some	O
DBMSs	O
that	O
are	O
specialized	O
for	O
warehousing	O
,	O
such	O
as	O
Sybase	B-Application
IQ	I-Application
,	O
use	O
columnar	O
storage	O
by	O
default	O
,	O
but	O
the	O
designer	O
still	O
sees	O
only	O
a	O
single	O
multi-column	O
table	O
.	O
</s>
<s>
Other	O
DBMSs	O
,	O
such	O
as	O
Microsoft	O
SQL	B-Language
Server	O
2012	O
and	O
later	O
,	O
let	O
you	O
specify	O
a	O
"	O
columnstore	O
index	O
"	O
for	O
a	O
particular	O
table	O
.	O
</s>
