<s>
The	O
database	B-Application
schema	I-Application
is	O
the	O
structure	O
of	O
a	O
database	O
described	O
in	O
a	O
formal	O
language	O
supported	O
by	O
the	O
database	B-Application
management	I-Application
system	I-Application
(	O
DBMS	O
)	O
.	O
</s>
<s>
The	O
term	O
"	O
schema	B-Application
"	O
refers	O
to	O
the	O
organization	O
of	O
data	O
as	O
a	O
blueprint	O
of	O
how	O
the	O
database	O
is	O
constructed	O
(	O
divided	O
into	O
database	B-Application
tables	I-Application
in	O
the	O
case	O
of	O
relational	B-Application
databases	I-Application
)	O
.	O
</s>
<s>
The	O
formal	O
definition	O
of	O
a	O
database	B-Application
schema	I-Application
is	O
a	O
set	O
of	O
formulas	O
(	O
sentences	O
)	O
called	O
integrity	O
constraints	O
imposed	O
on	O
a	O
database	O
.	O
</s>
<s>
These	O
integrity	O
constraints	O
ensure	O
compatibility	O
between	O
parts	O
of	O
the	O
schema	B-Application
.	O
</s>
<s>
The	O
states	O
of	O
a	O
created	O
conceptual	B-Application
schema	I-Application
are	O
transformed	O
into	O
an	O
explicit	O
mapping	O
,	O
the	O
database	B-Application
schema	I-Application
.	O
</s>
<s>
This	O
describes	O
how	O
real-world	O
entities	O
are	O
modeled	B-Application
in	O
the	O
database	O
.	O
</s>
<s>
"	O
A	O
database	B-Application
schema	I-Application
specifies	O
,	O
based	O
on	O
the	O
database	B-General_Concept
administrator	I-General_Concept
's	O
knowledge	O
of	O
possible	O
applications	O
,	O
the	O
facts	O
that	O
can	O
enter	O
the	O
database	O
,	O
or	O
those	O
of	O
interest	O
to	O
the	O
possible	O
end-users.	O
"	O
</s>
<s>
The	O
notion	O
of	O
a	O
database	B-Application
schema	I-Application
plays	O
the	O
same	O
role	O
as	O
the	O
notion	O
of	O
theory	O
in	O
predicate	B-Application
calculus	I-Application
.	O
</s>
<s>
Thus	O
a	O
schema	B-Application
can	O
contain	O
formulas	O
representing	O
integrity	O
constraints	O
specifically	O
for	O
an	O
application	O
and	O
the	O
constraints	O
specifically	O
for	O
a	O
type	O
of	O
database	O
,	O
all	O
expressed	O
in	O
the	O
same	O
database	O
language	O
.	O
</s>
<s>
In	O
a	O
relational	B-Application
database	I-Application
,	O
the	O
schema	B-Application
defines	O
the	O
tables	B-Application
,	O
fields	B-Application
,	O
relationships	O
,	O
views	B-Language
,	O
indexes	B-Data_Structure
,	O
packages	O
,	O
procedures	O
,	O
functions	O
,	O
queues	B-Application
,	O
triggers	O
,	O
types	O
,	O
sequences	O
,	O
materialized	B-Application
views	I-Application
,	O
synonyms	B-Application
,	O
database	O
links	O
,	O
directories	B-Application
,	O
XML	B-Language
schemas	I-Language
,	O
and	O
other	O
elements	O
.	O
</s>
<s>
A	O
database	O
generally	O
stores	O
its	O
schema	B-Application
in	O
a	O
data	B-Application
dictionary	I-Application
.	O
</s>
<s>
Although	O
a	O
schema	B-Application
is	O
defined	O
in	O
text	O
database	O
language	O
,	O
the	O
term	O
is	O
often	O
used	O
to	O
refer	O
to	O
a	O
graphical	O
depiction	O
of	O
the	O
database	O
structure	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
schema	B-Application
is	O
the	O
structure	O
of	O
the	O
database	O
that	O
defines	O
the	O
objects	O
in	O
the	O
database	O
.	O
</s>
<s>
In	O
an	O
Oracle	B-General_Concept
Database	I-General_Concept
system	O
,	O
the	O
term	O
"	O
schema	B-Application
"	O
has	O
a	O
slightly	O
different	O
connotation	O
.	O
</s>
<s>
The	O
requirements	O
listed	O
below	O
influence	O
the	O
detailed	O
structure	O
of	O
schemas	B-Application
that	O
are	O
produced	O
.	O
</s>
<s>
Each	O
of	O
the	O
overlapping	O
elements	O
specified	O
in	O
the	O
input	O
mapping	O
is	O
also	O
in	O
a	O
database	B-Application
schema	I-Application
relation	O
.	O
</s>
<s>
Source-specific	O
elements	O
that	O
are	O
associated	O
with	O
a	O
source	O
’s	O
overlapping	O
elements	O
are	O
passed	O
through	O
to	O
the	O
database	B-Application
schema	I-Application
.	O
</s>
<s>
Independent	O
entities	O
and	O
relationships	O
in	O
the	O
source	O
data	O
should	O
not	O
be	O
grouped	O
together	O
in	O
the	O
same	O
relation	O
in	O
the	O
database	B-Application
schema	I-Application
.	O
</s>
<s>
In	O
particular	O
,	O
source	O
specific	O
schema	B-Application
elements	O
should	O
not	O
be	O
grouped	O
with	O
overlapping	O
schema	B-Application
elements	O
,	O
if	O
the	O
grouping	O
co-locates	O
independent	O
entities	O
or	O
relationships	O
.	O
</s>
<s>
If	O
any	O
elements	O
of	O
the	O
database	B-Application
schema	I-Application
are	O
dropped	O
then	O
the	O
database	B-Application
schema	I-Application
is	O
not	O
ideal	O
.	O
</s>
<s>
Suppose	O
we	O
want	O
a	O
mediated	O
schema	B-Application
to	O
integrate	B-General_Concept
two	O
travel	O
databases	B-Application
,	O
Go-travel	O
and	O
Ok-flight	O
.	O
</s>
<s>
The	O
overlapping	O
information	O
in	O
Go-travel	O
’	O
s	O
and	O
Ok-flight	O
’	O
s	O
schemas	B-Application
could	O
be	O
represented	O
in	O
a	O
mediated	O
schema	B-Application
:	O
</s>
<s>
In	O
the	O
context	O
of	O
Oracle	B-General_Concept
Databases	I-General_Concept
,	O
a	O
schema	B-Application
object	I-Application
is	O
a	O
logical	O
data	B-General_Concept
storage	I-General_Concept
structure	I-General_Concept
.	O
</s>
<s>
An	O
Oracle	B-General_Concept
database	I-General_Concept
associates	O
a	O
separate	O
schema	B-Application
with	O
each	O
database	O
user	O
.	O
</s>
<s>
A	O
schema	B-Application
comprises	O
a	O
collection	O
of	O
schema	B-Application
objects	I-Application
.	O
</s>
<s>
Examples	O
of	O
schema	B-Application
objects	I-Application
include	O
:	O
</s>
<s>
Schema	B-Application
objects	I-Application
do	O
not	O
have	O
a	O
one-to-one	O
correspondence	O
to	O
physical	O
files	O
on	O
disk	O
that	O
store	O
their	O
information	O
.	O
</s>
<s>
However	O
,	O
Oracle	B-General_Concept
databases	I-General_Concept
store	O
schema	B-Application
objects	I-Application
logically	O
within	O
a	O
tablespace	B-General_Concept
of	O
the	O
database	O
.	O
</s>
<s>
The	O
data	O
of	O
each	O
object	O
is	O
physically	O
contained	O
in	O
one	O
or	O
more	O
of	O
the	O
tablespace	B-General_Concept
's	O
datafiles	B-General_Concept
.	O
</s>
<s>
For	O
some	O
objects	O
(	O
such	O
as	O
tables	B-Application
,	O
indexes	B-Data_Structure
,	O
and	O
clusters	O
)	O
a	O
database	B-General_Concept
administrator	I-General_Concept
can	O
specify	O
how	O
much	O
disk	O
space	O
the	O
Oracle	B-General_Concept
RDBMS	I-General_Concept
allocates	O
for	O
the	O
object	O
within	O
the	O
tablespace	B-General_Concept
's	O
datafiles	B-General_Concept
.	O
</s>
<s>
There	O
is	O
no	O
necessary	O
relationship	B-Architecture
between	O
schemas	B-Application
and	O
tablespaces	B-General_Concept
:	O
a	O
tablespace	B-General_Concept
can	O
contain	O
objects	O
from	O
different	O
schemas	B-Application
,	O
and	O
the	O
objects	O
for	O
a	O
single	O
schema	B-Application
can	O
reside	O
in	O
different	O
tablespaces	B-General_Concept
.	O
</s>
<s>
Oracle	B-General_Concept
database	I-General_Concept
specificity	O
does	O
,	O
however	O
,	O
enforce	O
platform	O
recognition	O
of	O
nonhomogenized	O
sequence	O
differentials	O
,	O
which	O
is	O
considered	O
a	O
crucial	O
limiting	O
factor	O
in	O
virtualized	O
applications	O
.	O
</s>
