<s>
Codd	B-Application
's	I-Application
twelve	I-Application
rules	I-Application
are	O
a	O
set	O
of	O
thirteen	O
rules	O
(	O
numbered	O
zero	O
to	O
twelve	O
)	O
proposed	O
by	O
Edgar	O
F	O
.	O
Codd	O
,	O
a	O
pioneer	O
of	O
the	O
relational	B-Architecture
model	I-Architecture
for	O
databases	B-Application
,	O
designed	O
to	O
define	O
what	O
is	O
required	O
from	O
a	O
database	B-Application
management	I-Application
system	I-Application
in	O
order	O
for	O
it	O
to	O
be	O
considered	O
relational	O
,	O
i.e.	O
,	O
a	O
relational	B-Application
database	I-Application
management	I-Application
system	I-Application
(	O
RDBMS	O
)	O
.	O
</s>
<s>
However	O
,	O
in	O
2007	O
another	O
textbook	O
stated	O
"	O
no	O
database	B-Application
system	I-Application
complies	O
with	O
all	O
twelve	O
rules	O
.	O
</s>
<s>
For	O
any	O
system	O
that	O
is	O
advertised	O
as	O
,	O
or	O
claimed	O
to	O
be	O
,	O
a	O
relational	O
data	B-Application
base	I-Application
management	I-Application
system	I-Application
,	O
that	O
system	O
must	O
be	O
able	O
to	O
manage	O
data	B-Application
bases	I-Application
entirely	O
through	O
its	O
relational	O
capabilities	O
.	O
</s>
<s>
All	O
information	O
in	O
a	O
relational	O
data	B-Application
base	I-Application
is	O
represented	O
explicitly	O
at	O
the	O
logical	O
level	O
and	O
in	O
exactly	O
one	O
way	O
by	O
values	O
in	O
tables	O
.	O
</s>
<s>
Each	O
and	O
every	O
datum	O
(	O
atomic	O
value	O
)	O
in	O
a	O
relational	O
data	B-Application
base	I-Application
is	O
guaranteed	O
to	O
be	O
logically	O
accessible	O
by	O
resorting	O
to	O
a	O
combination	O
of	O
table	O
name	O
,	O
primary	O
key	O
value	O
and	O
column	O
name	O
.	O
</s>
<s>
Rule	O
4	O
:	O
Dynamic	O
online	O
catalog	O
based	O
on	O
the	O
relational	B-Architecture
model	I-Architecture
:	O
</s>
<s>
The	O
data	B-Application
base	I-Application
description	O
is	O
represented	O
at	O
the	O
logical	O
level	O
in	O
the	O
same	O
way	O
as	O
ordinary	O
data	O
,	O
so	O
that	O
authorized	O
users	O
can	O
apply	O
the	O
same	O
relational	O
language	O
to	O
its	O
interrogation	O
as	O
they	O
apply	O
to	O
the	O
regular	O
data	O
.	O
</s>
<s>
View	B-Language
definition	O
.	O
</s>
<s>
Rule	O
6	O
:	O
The	O
view	B-Language
updating	O
rule	O
:	O
</s>
<s>
Integrity	O
constraints	O
specific	O
to	O
a	O
particular	O
relational	O
data	B-Application
base	I-Application
must	O
be	O
definable	O
in	O
the	O
relational	O
data	O
sublanguage	O
and	O
storable	O
in	O
the	O
catalog	O
,	O
not	O
in	O
the	O
application	O
programs	O
.	O
</s>
