<s>
In	O
data	B-General_Concept
management	I-General_Concept
and	O
database	O
analysis	O
,	O
a	O
data	B-Application
domain	I-Application
is	O
the	O
collection	O
of	O
values	O
that	O
a	O
data	O
element	O
may	O
contain	O
.	O
</s>
<s>
The	O
rule	O
for	O
determining	O
the	O
domain	O
boundary	O
may	O
be	O
as	O
simple	O
as	O
a	O
data	O
type	O
with	O
an	O
enumerated	B-Language
list	O
of	O
values	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
database	B-Application
table	I-Application
that	O
has	O
information	O
about	O
people	O
,	O
with	O
one	O
record	O
per	O
person	O
,	O
might	O
have	O
a	O
"	O
marital	O
status	O
"	O
column	O
.	O
</s>
<s>
This	O
column	O
might	O
be	O
declared	O
as	O
a	O
string	O
data	O
type	O
,	O
and	O
allowed	O
to	O
have	O
one	O
of	O
two	O
known	O
code	O
values	O
:	O
"	O
M	O
"	O
for	O
married	O
,	O
"	O
S	O
"	O
for	O
single	O
,	O
and	O
NULL	B-Language
for	O
records	O
where	O
marital	O
status	O
is	O
unknown	O
or	O
not	O
applicable	O
.	O
</s>
<s>
The	O
data	B-Application
domain	I-Application
for	O
the	O
marital	O
status	O
column	O
is	O
:	O
"	O
M	O
"	O
,	O
"	O
S	O
"	O
.	O
</s>
<s>
In	O
a	O
normalized	B-Application
data	I-Application
model	O
,	O
the	O
reference	B-General_Concept
domain	I-General_Concept
is	O
typically	O
specified	O
in	O
a	O
reference	B-General_Concept
table	I-General_Concept
.	O
</s>
<s>
Following	O
the	O
previous	O
example	O
,	O
a	O
Marital	O
Status	O
reference	B-General_Concept
table	I-General_Concept
would	O
have	O
exactly	O
two	O
records	O
,	O
one	O
per	O
allowed	O
value	O
—	O
excluding	O
NULL	B-Language
.	O
</s>
<s>
Reference	B-General_Concept
tables	I-General_Concept
are	O
formally	O
related	O
to	O
other	O
tables	O
in	O
a	O
database	O
by	O
the	O
use	O
of	O
foreign	B-Application
keys	I-Application
.	O
</s>
<s>
Less	O
simple	O
domain	O
boundary	O
rules	O
,	O
if	O
database-enforced	O
,	O
may	O
be	O
implemented	O
through	O
a	O
check	B-Language
constraint	I-Language
or	O
,	O
in	O
more	O
complex	O
cases	O
,	O
in	O
a	O
database	B-Language
trigger	I-Language
.	O
</s>
<s>
For	O
example	O
,	O
a	O
column	O
requiring	O
positive	O
numeric	O
values	O
may	O
have	O
a	O
check	B-Language
constraint	I-Language
declaring	O
that	O
the	O
values	O
must	O
be	O
greater	O
than	O
zero	O
.	O
</s>
<s>
This	O
definition	O
combines	O
the	O
concepts	O
of	O
domain	O
as	O
an	O
area	O
over	O
which	O
control	O
is	O
exercised	O
and	O
the	O
mathematical	O
idea	O
of	O
a	O
set	O
of	O
values	O
of	O
an	O
independent	O
variable	O
for	O
which	O
a	O
function	O
is	O
defined	O
,	O
as	O
in	O
Domain	B-Algorithm
of	I-Algorithm
a	I-Algorithm
function	I-Algorithm
.	O
</s>
