<s>
A	O
conceptual	B-Application
schema	I-Application
is	O
a	O
high-level	O
description	O
of	O
informational	O
needs	O
underlying	O
the	O
design	O
of	O
a	O
database	O
.	O
</s>
<s>
It	O
typically	O
includes	O
only	O
the	O
main	O
concepts	O
and	O
the	O
main	O
relationships	B-Architecture
among	O
them	O
.	O
</s>
<s>
The	O
conceptual	B-Application
model	I-Application
is	O
also	O
known	O
as	O
the	O
data	B-Application
model	I-Application
that	O
can	O
be	O
used	O
to	O
describe	O
the	O
conceptual	B-Application
schema	I-Application
when	O
a	O
database	O
system	O
is	O
implemented	O
.	O
</s>
<s>
It	O
hides	O
the	O
internal	O
details	O
of	O
physical	O
storage	O
and	O
targets	O
on	O
describing	O
entities	O
,	O
datatypes	O
,	O
relationships	B-Architecture
and	O
constraints	O
.	O
</s>
<s>
A	O
conceptual	B-Application
schema	I-Application
or	O
conceptual	B-Application
data	I-Application
model	I-Application
is	O
a	O
map	O
of	O
concepts	O
and	O
their	O
relationships	B-Architecture
used	O
for	O
databases	O
.	O
</s>
<s>
This	O
describes	O
the	O
semantics	B-Application
of	O
an	O
organization	O
and	O
represents	O
a	O
series	O
of	O
assertions	O
about	O
its	O
nature	O
.	O
</s>
<s>
Specifically	O
,	O
it	O
describes	O
the	O
things	O
of	O
significance	O
to	O
an	O
organization	O
(	O
entity	O
classes	O
)	O
,	O
about	O
which	O
it	O
is	O
inclined	O
to	O
collect	O
information	O
,	O
and	O
its	O
characteristics	O
(	O
attributes	O
)	O
and	O
the	O
associations	O
between	O
pairs	O
of	O
those	O
things	O
of	O
significance	O
(	O
relationships	B-Architecture
)	O
.	O
</s>
<s>
Because	O
a	O
conceptual	B-Application
schema	I-Application
represents	O
the	O
semantics	B-Application
of	O
an	O
organization	O
,	O
and	O
not	O
a	O
database	B-General_Concept
design	I-General_Concept
,	O
it	O
may	O
exist	O
on	O
various	O
levels	O
of	O
abstraction	O
.	O
</s>
<s>
These	O
are	O
consolidated	O
into	O
a	O
single	O
conceptual	B-Application
schema	I-Application
that	O
is	O
the	O
superset	O
of	O
all	O
of	O
those	O
external	O
views	O
.	O
</s>
<s>
A	O
data	B-Application
model	I-Application
can	O
be	O
as	O
concrete	O
as	O
each	O
person	O
's	O
perspective	O
,	O
but	O
this	O
tends	O
to	O
make	O
it	O
inflexible	O
.	O
</s>
<s>
Conceptual	B-Application
data	I-Application
models	I-Application
take	O
a	O
more	O
abstract	O
perspective	O
,	O
identifying	O
the	O
fundamental	O
things	O
,	O
of	O
which	O
the	O
things	O
an	O
individual	O
deals	O
with	O
are	O
just	O
examples	O
.	O
</s>
<s>
The	O
model	O
does	O
allow	O
for	O
what	O
is	O
called	O
inheritance	B-Language
in	O
object	B-Language
oriented	I-Language
terms	O
.	O
</s>
<s>
The	O
set	O
of	O
instances	O
of	O
an	O
entity	B-Architecture
class	I-Architecture
may	O
be	O
subdivided	O
into	O
entity	O
classes	O
in	O
their	O
own	O
right	O
.	O
</s>
<s>
Thus	O
,	O
each	O
instance	O
of	O
a	O
sub-type	O
entity	B-Architecture
class	I-Architecture
is	O
also	O
an	O
instance	O
of	O
the	O
entity	B-Architecture
class	I-Architecture
's	O
super-type	O
.	O
</s>
<s>
Each	O
instance	O
of	O
the	O
super-type	O
entity	B-Architecture
class	I-Architecture
,	O
then	O
is	O
also	O
an	O
instance	O
of	O
one	O
of	O
the	O
sub-type	O
entity	O
classes	O
.	O
</s>
<s>
Super-type/sub	O
-type	O
relationships	B-Architecture
may	O
be	O
exclusive	B-General_Concept
or	O
not	O
.	O
</s>
<s>
A	O
data	B-Application
structure	I-Application
diagram	I-Application
(	O
DSD	O
)	O
is	O
a	O
data	B-Application
model	I-Application
or	O
diagram	O
used	O
to	O
describe	O
conceptual	B-Application
data	I-Application
models	I-Application
by	O
providing	O
graphical	O
notations	O
which	O
document	O
entities	O
and	O
their	O
relationships	B-Architecture
,	O
and	O
the	O
constraints	O
that	O
bind	O
them	O
.	O
</s>
