<s>
The	O
three-schema	B-Application
approach	I-Application
,	O
or	O
three-schema	O
concept	O
,	O
in	O
software	B-General_Concept
engineering	I-General_Concept
is	O
an	O
approach	O
to	O
building	O
information	O
systems	O
and	O
systems	O
information	B-Application
management	I-Application
that	O
originated	O
in	O
the	O
1970s	O
.	O
</s>
<s>
It	O
proposes	O
three	O
different	O
views	B-Architecture
in	O
systems	O
development	O
,	O
with	O
conceptual	O
modelling	O
being	O
considered	O
the	O
key	O
to	O
achieving	O
data	B-General_Concept
integration	I-General_Concept
.	O
</s>
<s>
The	O
three-schema	B-Application
approach	I-Application
provides	O
for	O
three	O
types	O
of	O
schemas	O
with	O
schema	O
techniques	O
based	O
on	O
formal	O
language	O
descriptions	O
:	O
</s>
<s>
At	O
the	O
center	O
,	O
the	O
conceptual	B-Application
schema	I-Application
defines	O
the	O
ontology	O
of	O
the	O
concepts	O
as	O
the	O
users	O
think	O
of	O
them	O
and	O
talk	O
about	O
them	O
.	O
</s>
<s>
The	O
framework	O
attempted	O
to	O
permit	O
multiple	O
data	B-Application
models	I-Application
to	O
be	O
used	O
for	O
external	O
schemata	O
.	O
</s>
<s>
However	O
,	O
for	O
the	O
most	O
part	O
,	O
the	O
traditional	O
approach	O
to	O
building	O
systems	O
has	O
only	O
focused	O
on	O
defining	O
data	O
from	O
two	O
distinct	O
views	B-Architecture
,	O
the	O
"	O
user	O
view	O
"	O
and	O
the	O
"	O
computer	O
view	O
"	O
.	O
</s>
<s>
The	O
required	O
structure	O
of	O
data	O
for	O
computer	B-General_Concept
storage	I-General_Concept
depends	O
upon	O
the	O
specific	O
computer	O
technology	O
employed	O
and	O
the	O
need	O
for	O
efficient	O
processing	O
of	O
data	O
.	O
</s>
<s>
These	O
two	O
traditional	O
views	B-Architecture
of	O
data	O
have	O
been	O
defined	O
by	O
analysts	O
over	O
the	O
years	O
on	O
an	O
application	O
by	O
application	O
basis	O
as	O
specific	O
business	O
needs	O
were	O
addressed	O
,	O
see	O
Figure	O
1	O
.	O
</s>
<s>
The	O
need	O
for	O
flexibility	O
,	O
however	O
,	O
led	O
to	O
the	O
introduction	O
of	O
Database	B-Application
Management	I-Application
Systems	I-Application
(	O
DBMSs	O
)	O
,	O
which	O
allow	O
for	O
random	O
access	O
of	O
logically	O
connected	O
pieces	O
of	O
data	O
.	O
</s>
<s>
Furthermore	O
,	O
most	O
large	O
companies	O
have	O
had	O
to	O
develop	O
multiple	O
databases	B-Application
which	O
are	O
often	O
under	O
the	O
control	O
of	O
different	O
DBMSs	O
and	O
still	O
have	O
the	O
problems	O
of	O
redundancy	O
and	O
inconsistency	O
.	O
</s>
<s>
The	O
recognition	O
of	O
this	O
problem	O
led	O
the	O
ANSI/X3/SPARC	O
Study	O
Group	O
on	O
Database	B-Application
Management	I-Application
Systems	I-Application
to	O
conclude	O
that	O
in	O
an	O
ideal	O
data	O
management	O
environment	O
a	O
third	O
view	O
of	O
data	O
is	O
needed	O
.	O
</s>
<s>
This	O
view	O
,	O
referred	O
to	O
as	O
a	O
"	O
conceptual	B-Application
schema	I-Application
"	O
is	O
a	O
single	O
integrated	O
definition	O
of	O
the	O
data	O
within	O
an	O
enterprise	O
which	O
is	O
unbiased	O
toward	O
any	O
single	O
application	O
of	O
data	O
and	O
is	O
independent	O
of	O
how	O
the	O
data	O
is	O
physically	O
stored	O
or	O
accessed	O
,	O
see	O
Figure	O
2	O
.	O
</s>
<s>
The	O
primary	O
objective	O
of	O
this	O
conceptual	B-Application
schema	I-Application
is	O
to	O
provide	O
a	O
consistent	O
definition	O
of	O
the	O
meanings	O
and	O
interrelationship	O
of	O
data	O
which	O
can	O
be	O
used	O
to	O
integrate	O
,	O
share	O
,	O
and	O
manage	O
the	O
integrity	O
of	O
data	O
.	O
</s>
<s>
The	O
notion	O
of	O
a	O
three-schema	O
model	O
consisting	O
of	O
a	O
conceptual	B-Application
model	I-Application
,	O
an	O
external	O
model	O
,	O
and	O
an	O
internal	O
or	O
physical	O
model	O
was	O
first	O
introduced	O
by	O
the	O
ANSI/X3/SPARC	O
Standards	O
Planning	O
and	O
Requirements	O
Committee	O
directed	O
by	O
Charles	O
Bachman	O
in	O
1975	O
.	O
</s>
<s>
The	O
conceptual	B-Application
schema	I-Application
represents	O
the	O
basic	O
underlying	O
structure	O
of	O
data	O
as	O
viewed	O
by	O
the	O
enterprise	O
as	O
a	O
whole	O
.	O
</s>
<s>
Over	O
the	O
next	O
twenty	O
years	O
,	O
various	O
groups	O
attempted	O
to	O
define	O
standards	O
for	O
the	O
conceptual	B-Application
schema	I-Application
and	O
its	O
mappings	O
to	O
databases	B-Application
and	O
programming	O
languages	O
.	O
</s>
<s>
The	O
conceptual	B-Application
model	I-Application
represents	O
the	O
view	O
of	O
data	O
that	O
is	O
negotiated	O
between	O
end	O
users	O
and	O
database	O
administrators	O
covering	O
those	O
entities	O
about	O
which	O
it	O
is	O
important	O
to	O
keep	O
data	O
,	O
the	O
meaning	O
of	O
the	O
data	O
,	O
and	O
the	O
relationships	O
of	O
the	O
data	O
to	O
each	O
other	O
.	O
</s>
<s>
One	O
further	O
development	O
is	O
the	O
IDEF1X	B-Application
information	O
modeling	O
methodology	O
,	O
which	O
is	O
based	O
on	O
the	O
three-schema	O
concept	O
.	O
</s>
<s>
Another	O
is	O
the	O
Zachman	B-Library
Framework	I-Library
,	O
proposed	O
by	O
John	O
Zachman	O
in	O
1987	O
and	O
developed	O
ever	O
since	O
in	O
the	O
field	O
of	O
Enterprise	O
Architecture	O
.	O
</s>
<s>
In	O
other	O
Enterprise	B-Library
Architecture	I-Library
frameworks	I-Library
some	O
kind	O
of	O
view	B-Architecture
model	I-Architecture
is	O
incorporated	O
.	O
</s>
