<s>
A	O
data	B-Application
dictionary	I-Application
,	O
or	O
metadata	B-Application
repository	I-Application
,	O
as	O
defined	O
in	O
the	O
IBM	O
Dictionary	O
of	O
Computing	O
,	O
is	O
a	O
"	O
centralized	O
repository	O
of	O
information	O
about	O
data	O
such	O
as	O
meaning	O
,	O
relationships	O
to	O
other	O
data	O
,	O
origin	O
,	O
usage	O
,	O
and	O
format	O
"	O
.	O
</s>
<s>
Oracle	B-General_Concept
defines	O
it	O
as	O
a	O
collection	O
of	O
tables	B-Application
with	O
metadata	O
.	O
</s>
<s>
The	O
term	O
can	O
have	O
one	O
of	O
several	O
closely	O
related	O
meanings	O
pertaining	O
to	O
databases	B-Application
and	O
database	B-Application
management	I-Application
systems	I-Application
(	O
DBMS	B-Application
)	O
:	O
</s>
<s>
The	O
terms	O
data	B-Application
dictionary	I-Application
and	O
data	O
repository	O
indicate	O
a	O
more	O
general	O
software	O
utility	O
than	O
a	O
catalogue	O
.	O
</s>
<s>
A	O
catalogue	O
is	O
closely	O
coupled	O
with	O
the	O
DBMS	B-Application
software	O
.	O
</s>
<s>
It	O
provides	O
the	O
information	O
stored	O
in	O
it	O
to	O
the	O
user	O
and	O
the	O
DBA	O
,	O
but	O
it	O
is	O
mainly	O
accessed	O
by	O
the	O
various	O
software	O
modules	O
of	O
the	O
DBMS	B-Application
itself	O
,	O
such	O
as	O
DDL	B-Language
and	O
DML	B-Language
compilers	O
,	O
the	O
query	B-Language
optimiser	O
,	O
the	O
transaction	O
processor	O
,	O
report	O
generators	O
,	O
and	O
the	O
constraint	O
enforcer	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
a	O
data	B-Application
dictionary	I-Application
is	O
a	O
data	O
structure	O
that	O
stores	O
metadata	O
,	O
i.e.	O
,	O
(	O
structured	O
)	O
data	O
about	O
information	O
.	O
</s>
<s>
The	O
software	O
package	O
for	O
a	O
stand-alone	O
data	B-Application
dictionary	I-Application
or	O
data	O
repository	O
may	O
interact	O
with	O
the	O
software	O
modules	O
of	O
the	O
DBMS	B-Application
,	O
but	O
it	O
is	O
mainly	O
used	O
by	O
the	O
designers	O
,	O
users	O
and	O
administrators	O
of	O
a	O
computer	O
system	O
for	O
information	O
resource	O
management	O
.	O
</s>
<s>
These	O
systems	O
maintain	O
information	O
on	O
system	O
hardware	O
and	O
software	O
configuration	O
,	O
documentation	O
,	O
application	B-Application
and	O
users	O
as	O
well	O
as	O
other	O
information	O
relevant	O
to	O
system	O
administration	O
.	O
</s>
<s>
If	O
a	O
data	B-Application
dictionary	I-Application
system	O
is	O
used	O
only	O
by	O
the	O
designers	O
,	O
users	O
,	O
and	O
administrators	O
and	O
not	O
by	O
the	O
DBMS	B-Application
Software	O
,	O
it	O
is	O
called	O
a	O
passive	O
data	B-Application
dictionary	I-Application
.	O
</s>
<s>
Otherwise	O
,	O
it	O
is	O
called	O
an	O
active	O
data	B-Application
dictionary	I-Application
or	O
data	B-Application
dictionary	I-Application
.	O
</s>
<s>
When	O
a	O
passive	O
data	B-Application
dictionary	I-Application
is	O
updated	O
,	O
it	O
is	O
done	O
so	O
manually	O
and	O
independently	O
from	O
any	O
changes	O
to	O
a	O
DBMS	B-Application
(	O
database	O
)	O
structure	O
.	O
</s>
<s>
With	O
an	O
active	O
data	B-Application
dictionary	I-Application
,	O
the	O
dictionary	O
is	O
updated	O
first	O
and	O
changes	O
occur	O
in	O
the	O
DBMS	B-Application
automatically	O
as	O
a	O
result	O
.	O
</s>
<s>
Database	O
users	O
and	O
application	B-Application
developers	O
can	O
benefit	O
from	O
an	O
authoritative	O
data	B-Application
dictionary	I-Application
document	O
that	O
catalogs	O
the	O
organization	O
,	O
contents	O
,	O
and	O
conventions	O
of	O
one	O
or	O
more	O
databases	B-Application
.	O
</s>
<s>
This	O
typically	O
includes	O
the	O
names	O
and	O
descriptions	O
of	O
various	O
tables	B-Application
(	O
records	B-Application
or	O
entities	O
)	O
and	O
their	O
contents	O
(	O
fields	B-Application
)	O
plus	O
additional	O
details	O
,	O
like	O
the	O
type	O
and	O
length	O
of	O
each	O
data	O
element	O
.	O
</s>
<s>
Another	O
important	O
piece	O
of	O
information	O
that	O
a	O
data	B-Application
dictionary	I-Application
can	O
provide	O
is	O
the	O
relationship	O
between	O
tables	B-Application
.	O
</s>
<s>
This	O
is	O
sometimes	O
referred	O
to	O
in	O
entity-relationship	B-Architecture
diagrams	I-Architecture
(	O
ERDs	O
)	O
,	O
or	O
if	O
using	O
set	O
descriptors	O
,	O
identifying	O
which	O
sets	O
database	B-Application
tables	I-Application
participate	O
in	O
.	O
</s>
<s>
In	O
an	O
active	O
data	B-Application
dictionary	I-Application
constraints	O
may	O
be	O
placed	O
upon	O
the	O
underlying	O
data	O
.	O
</s>
<s>
Additionally	O
,	O
a	O
distributed	O
DBMS	B-Application
may	O
have	O
certain	O
location	O
specifics	O
described	O
within	O
its	O
active	O
data	B-Application
dictionary	I-Application
(	O
e.g.	O
</s>
<s>
where	O
tables	B-Application
are	O
physically	O
located	O
)	O
.	O
</s>
<s>
The	O
data	B-Application
dictionary	I-Application
consists	O
of	O
record	O
types	O
(	O
tables	B-Application
)	O
created	O
in	O
the	O
database	O
by	O
systems	O
generated	O
command	O
files	O
,	O
tailored	O
for	O
each	O
supported	O
back-end	O
DBMS	B-Application
.	O
</s>
<s>
Oracle	B-General_Concept
has	O
a	O
list	O
of	O
specific	O
views	O
for	O
the	O
"	O
sys	O
"	O
user	O
.	O
</s>
<s>
In	O
the	O
construction	O
of	O
database	O
applications	O
,	O
it	O
can	O
be	O
useful	O
to	O
introduce	O
an	O
additional	O
layer	O
of	O
data	B-Application
dictionary	I-Application
software	O
,	O
i.e.	O
</s>
<s>
middleware	B-General_Concept
,	O
which	O
communicates	O
with	O
the	O
underlying	O
DBMS	B-Application
data	B-Application
dictionary	I-Application
.	O
</s>
<s>
Such	O
a	O
"	O
high-level	O
"	O
data	B-Application
dictionary	I-Application
may	O
offer	O
additional	O
features	O
and	O
a	O
degree	O
of	O
flexibility	O
that	O
goes	O
beyond	O
the	O
limitations	O
of	O
the	O
native	O
"	O
low-level	O
"	O
data	B-Application
dictionary	I-Application
,	O
whose	O
primary	O
purpose	O
is	O
to	O
support	O
the	O
basic	O
functions	O
of	O
the	O
DBMS	B-Application
,	O
not	O
the	O
requirements	O
of	O
a	O
typical	O
application	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
a	O
high-level	O
data	B-Application
dictionary	I-Application
can	O
provide	O
alternative	O
entity-relationship	B-Architecture
models	I-Architecture
tailored	O
to	O
suit	O
different	O
applications	O
that	O
share	O
a	O
common	O
database	O
.	O
</s>
<s>
Extensions	O
to	O
the	O
data	B-Application
dictionary	I-Application
also	O
can	O
assist	O
in	O
query	B-Language
optimization	I-Language
against	O
distributed	B-Operating_System
databases	I-Operating_System
.	O
</s>
<s>
Additionally	O
,	O
DBA	O
functions	O
are	O
often	O
automated	O
using	O
restructuring	O
tools	O
that	O
are	O
tightly	O
coupled	O
to	O
an	O
active	O
data	B-Application
dictionary	I-Application
.	O
</s>
<s>
Software	B-Architecture
frameworks	I-Architecture
aimed	O
at	O
rapid	O
application	B-Application
development	O
sometimes	O
include	O
high-level	O
data	B-Application
dictionary	I-Application
facilities	O
,	O
which	O
can	O
substantially	O
reduce	O
the	O
amount	O
of	O
programming	O
required	O
to	O
build	O
menus	O
,	O
forms	B-Language
,	O
reports	O
,	O
and	O
other	O
components	O
of	O
a	O
database	O
application	B-Application
,	O
including	O
the	O
database	O
itself	O
.	O
</s>
<s>
For	O
example	O
,	O
PHPLens	O
includes	O
a	O
PHP	B-Application
class	I-Application
library	O
to	O
automate	O
the	O
creation	O
of	O
tables	B-Application
,	O
indexes	O
,	O
and	O
foreign	B-Application
key	I-Application
constraints	I-Application
portably	B-Architecture
for	O
multiple	O
databases	B-Application
.	O
</s>
<s>
Another	O
PHP-based	O
data	B-Application
dictionary	I-Application
,	O
part	O
of	O
the	O
RADICORE	O
toolkit	O
,	O
automatically	O
generates	O
program	O
objects	O
,	O
scripts	B-Language
,	O
and	O
SQL	O
code	O
for	O
menus	O
and	O
forms	B-Language
with	O
data	O
validation	O
and	O
complex	O
joins	B-Language
.	O
</s>
<s>
For	O
the	O
ASP.NET	B-Application
environment	O
,	O
Base	O
One	O
's	O
data	B-Application
dictionary	I-Application
provides	O
cross-DBMS	O
facilities	O
for	O
automated	O
database	O
creation	O
,	O
data	O
validation	O
,	O
performance	O
enhancement	O
(	O
caching	B-General_Concept
and	O
index	O
utilization	O
)	O
,	O
application	B-Application
security	O
,	O
and	O
extended	O
data	O
types	O
.	O
</s>
<s>
Visual	B-Application
DataFlex	I-Application
features	O
provides	O
the	O
ability	O
to	O
use	O
DataDictionaries	O
as	O
class	O
files	O
to	O
form	O
middle	O
layer	O
between	O
the	O
user	O
interface	O
and	O
the	O
underlying	O
database	O
.	O
</s>
<s>
Some	O
industries	O
use	O
generalized	O
data	B-Application
dictionaries	I-Application
as	O
technical	O
standards	O
to	O
ensure	O
interoperability	O
between	O
systems	O
.	O
</s>
<s>
This	O
intermediate	O
mapping	O
layer	O
for	O
MLSs	O
 '	O
native	O
databases	B-Application
is	O
supported	O
by	O
software	O
companies	O
which	O
provide	O
API	O
services	O
to	O
MLS	O
organizations	O
.	O
</s>
<s>
Developers	O
use	O
a	O
data	O
description	O
specification	O
(	O
DDS	O
)	O
to	O
describe	O
data	O
attributes	O
in	O
file	O
descriptions	O
that	O
are	O
external	O
to	O
the	O
application	B-Application
program	I-Application
that	O
processes	O
the	O
data	O
,	O
in	O
the	O
context	O
of	O
an	O
IBM	B-Application
i	I-Application
.	O
</s>
<s>
The	O
sys.ts	O
$	O
table	O
in	O
Oracle	B-General_Concept
stores	O
information	O
about	O
every	O
table	O
in	O
the	O
database	O
.	O
</s>
<s>
It	O
is	O
part	O
of	O
the	O
data	B-Application
dictionary	I-Application
that	O
is	O
created	O
when	O
the	O
Oracle	B-General_Concept
Database	I-General_Concept
is	O
created	O
.	O
</s>
<s>
Developers	O
may	O
also	O
use	O
DDS	O
context	O
from	O
free	B-License
and	I-License
open-source	I-License
software	I-License
(	O
FOSS	B-License
)	O
for	O
structured	O
and	O
transactional	O
queries	B-Language
in	O
open	O
environments	O
.	O
</s>
<s>
Here	O
is	O
a	O
non-exhaustive	O
list	O
of	O
typical	O
items	O
found	O
in	O
a	O
data	B-Application
dictionary	I-Application
for	O
columns	O
or	O
fields	B-Application
:	O
</s>
<s>
Reference	O
table	O
name	O
,	O
if	O
a	O
foreign	B-Application
key	I-Application
.	O
</s>
<s>
See	O
event-driven	B-Application
programming	I-Application
.	O
</s>
