<s>
A	O
physical	B-Application
data	I-Application
model	I-Application
(	O
or	O
database	B-General_Concept
design	I-General_Concept
)	O
is	O
a	O
representation	O
of	O
a	O
data	O
design	O
as	O
implemented	O
,	O
or	O
intended	O
to	O
be	O
implemented	O
,	O
in	O
a	O
database	B-Application
management	I-Application
system	I-Application
.	O
</s>
<s>
In	O
the	O
lifecycle	B-General_Concept
of	I-General_Concept
a	I-General_Concept
project	I-General_Concept
it	O
typically	O
derives	O
from	O
a	O
logical	B-Application
data	I-Application
model	I-Application
,	O
though	O
it	O
may	O
be	O
reverse-engineered	O
from	O
a	O
given	O
database	O
implementation	O
.	O
</s>
<s>
A	O
complete	O
physical	B-Application
data	I-Application
model	I-Application
will	O
include	O
all	O
the	O
database	O
artifacts	O
required	O
to	O
create	O
relationships	B-Application
between	I-Application
tables	I-Application
or	O
to	O
achieve	O
performance	O
goals	O
,	O
such	O
as	O
indexes	O
,	O
constraint	O
definitions	O
,	O
linking	O
tables	O
,	O
partitioned	B-General_Concept
tables	I-General_Concept
or	O
clusters	O
.	O
</s>
<s>
Analysts	O
can	O
usually	O
use	O
a	O
physical	B-Application
data	I-Application
model	I-Application
to	O
calculate	O
storage	O
estimates	O
;	O
it	O
may	O
include	O
specific	O
storage	O
allocation	O
details	O
for	O
a	O
given	O
database	B-Application
system	I-Application
.	O
</s>
<s>
seven	O
main	O
databases	B-Application
dominate	O
the	O
commercial	O
marketplace	O
:	O
Informix	B-Application
,	O
Oracle	B-General_Concept
,	O
Postgres	B-Application
,	O
SQL	B-Application
Server	I-Application
,	O
Sybase	B-Application
,	O
IBM	B-Application
Db2	I-Application
and	O
MySQL	B-Application
.	O
</s>
<s>
Other	O
RDBMS	O
systems	O
tend	O
either	O
to	O
be	O
legacy	O
databases	B-Application
or	O
used	O
within	O
academia	O
such	O
as	O
universities	O
or	O
further	O
education	O
colleges	O
.	O
</s>
<s>
Physical	B-Application
data	I-Application
models	I-Application
for	O
each	O
implementation	O
would	O
differ	O
significantly	O
,	O
not	O
least	O
due	O
to	O
underlying	O
operating-system	O
requirements	O
that	O
may	O
sit	O
underneath	O
them	O
.	O
</s>
<s>
For	O
example	O
:	O
SQL	B-Application
Server	I-Application
runs	O
only	O
on	O
Microsoft	B-Application
Windows	I-Application
operating-systems	O
(	O
Starting	O
with	O
SQL	B-Application
Server	I-Application
2017	O
,	O
SQL	B-Application
Server	I-Application
runs	O
on	O
Linux	O
.	O
</s>
<s>
It	O
's	O
the	O
same	O
SQL	B-Application
Server	I-Application
database	O
engine	O
,	O
with	O
many	O
similar	O
features	O
and	O
services	O
regardless	O
of	O
your	O
operating	O
system	O
)	O
,	O
while	O
Oracle	B-General_Concept
and	O
MySQL	B-Application
can	O
run	O
on	O
Solaris	O
,	O
Linux	O
and	O
other	O
UNIX-based	O
operating-systems	O
as	O
well	O
as	O
on	O
Windows	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
disk	O
requirements	O
,	O
security	O
requirements	O
and	O
many	O
other	O
aspects	O
of	O
a	O
physical	B-Application
data	I-Application
model	I-Application
will	O
be	O
influenced	O
by	O
the	O
RDBMS	O
that	O
a	O
database	B-General_Concept
administrator	I-General_Concept
(	O
or	O
an	O
organization	O
)	O
chooses	O
to	O
use	O
.	O
</s>
<s>
Physical	B-Application
schema	I-Application
is	O
a	O
term	O
used	O
in	O
data	B-General_Concept
management	I-General_Concept
to	O
describe	O
how	O
data	O
is	O
to	O
be	O
represented	O
and	O
stored	O
(	O
files	O
,	O
indices	O
,	O
et	O
al	O
.	O
)	O
</s>
<s>
in	O
secondary	O
storage	O
using	O
a	O
particular	O
database	B-Application
management	I-Application
system	I-Application
(	O
DBMS	O
)	O
(	O
e.g.	O
,	O
Oracle	B-General_Concept
RDBMS	I-General_Concept
,	O
Sybase	B-Application
SQL	I-Application
Server	I-Application
,	O
etc	O
.	O
</s>
<s>
In	O
the	O
ANSI/SPARC	B-General_Concept
Architecture	I-General_Concept
three	B-Application
schema	I-Application
approach	I-Application
,	O
the	O
internal	O
schema	B-Application
is	O
the	O
view	O
of	O
data	O
that	O
involved	O
data	B-General_Concept
management	I-General_Concept
technology	O
.	O
</s>
<s>
This	O
is	O
as	O
opposed	O
to	O
an	O
external	O
schema	B-Application
that	O
reflects	O
an	O
individual	O
's	O
view	O
of	O
the	O
data	O
,	O
or	O
the	O
conceptual	B-Application
schema	I-Application
that	O
is	O
the	O
integration	O
of	O
a	O
set	O
of	O
external	O
schemas	B-Application
.	O
</s>
<s>
Subsequently	O
the	O
internal	O
schema	B-Application
was	O
recognized	O
to	O
have	O
two	O
parts	O
:	O
</s>
<s>
The	O
logical	B-Application
schema	I-Application
was	O
the	O
way	O
data	O
were	O
represented	O
to	O
conform	O
to	O
the	O
constraints	O
of	O
a	O
particular	O
approach	O
to	O
database	B-Application
management	I-Application
.	O
</s>
<s>
Describing	O
the	O
logical	B-Application
schema	I-Application
,	O
however	O
,	O
still	O
did	O
not	O
describe	O
how	O
physically	O
data	O
would	O
be	O
stored	O
on	O
disk	O
drives	O
.	O
</s>
<s>
That	O
is	O
the	O
domain	O
of	O
the	O
physical	B-Application
schema	I-Application
.	O
</s>
<s>
Now	O
logical	B-Application
schemas	I-Application
describe	O
data	O
in	O
terms	O
of	O
relational	O
tables	O
and	O
columns	O
,	O
object-oriented	O
classes	O
,	O
and	O
XML	B-Protocol
tags	O
.	O
</s>
