<s>
In	O
computing	O
,	O
a	O
database	O
is	O
an	O
organized	O
collection	O
of	O
data	B-General_Concept
stored	O
and	O
accessed	O
electronically	O
.	O
</s>
<s>
Small	O
databases	B-Application
can	O
be	O
stored	O
on	O
a	O
file	B-Application
system	I-Application
,	O
while	O
large	O
databases	B-Application
are	O
hosted	O
on	O
computer	B-Architecture
clusters	I-Architecture
or	O
cloud	O
storage	O
.	O
</s>
<s>
The	O
design	B-General_Concept
of	I-General_Concept
databases	I-General_Concept
spans	O
formal	O
techniques	O
and	O
practical	O
considerations	O
,	O
including	O
data	B-Application
modeling	I-Application
,	O
efficient	O
data	B-General_Concept
representation	O
and	O
storage	O
,	O
query	B-Language
languages	I-Language
,	O
security	O
and	O
privacy	O
of	O
sensitive	O
data	B-General_Concept
,	O
and	O
distributed	B-Architecture
computing	I-Architecture
issues	O
,	O
including	O
supporting	O
concurrent	B-Operating_System
access	I-Operating_System
and	O
fault	B-General_Concept
tolerance	I-General_Concept
.	O
</s>
<s>
A	O
database	B-Application
management	I-Application
system	I-Application
(	O
DBMS	B-General_Concept
)	O
is	O
the	O
software	O
that	O
interacts	O
with	O
end	O
users	O
,	O
applications	O
,	O
and	O
the	O
database	O
itself	O
to	O
capture	O
and	O
analyze	O
the	O
data	B-General_Concept
.	O
</s>
<s>
The	O
DBMS	B-General_Concept
software	O
additionally	O
encompasses	O
the	O
core	O
facilities	O
provided	O
to	O
administer	O
the	O
database	O
.	O
</s>
<s>
The	O
sum	O
total	O
of	O
the	O
database	O
,	O
the	O
DBMS	B-General_Concept
and	O
the	O
associated	O
applications	O
can	O
be	O
referred	O
to	O
as	O
a	O
database	B-Application
system	I-Application
.	O
</s>
<s>
Often	O
the	O
term	O
"	O
database	O
"	O
is	O
also	O
used	O
loosely	O
to	O
refer	O
to	O
any	O
of	O
the	O
DBMS	B-General_Concept
,	O
the	O
database	B-Application
system	I-Application
or	O
an	O
application	O
associated	O
with	O
the	O
database	O
.	O
</s>
<s>
Computer	B-General_Concept
scientists	I-General_Concept
may	O
classify	O
database	B-Application
management	I-Application
systems	I-Application
according	O
to	O
the	O
database	B-General_Concept
models	I-General_Concept
that	O
they	O
support	O
.	O
</s>
<s>
Relational	B-Application
databases	I-Application
became	O
dominant	O
in	O
the	O
1980s	O
.	O
</s>
<s>
These	O
model	O
data	B-General_Concept
as	O
rows	B-Application
and	O
columns	B-Application
in	O
a	O
series	O
of	O
tables	B-Application
,	O
and	O
the	O
vast	O
majority	O
use	O
SQL	B-Language
for	O
writing	O
and	O
querying	O
data	B-General_Concept
.	O
</s>
<s>
In	O
the	O
2000s	O
,	O
non-relational	B-General_Concept
databases	I-General_Concept
became	O
popular	O
,	O
collectively	O
referred	O
to	O
as	O
NoSQL	B-General_Concept
,	O
because	O
they	O
use	O
different	O
query	B-Language
languages	I-Language
.	O
</s>
<s>
Formally	O
,	O
a	O
"	O
database	O
"	O
refers	O
to	O
a	O
set	O
of	O
related	O
data	B-General_Concept
and	O
the	O
way	O
it	O
is	O
organized	O
.	O
</s>
<s>
Access	O
to	O
this	O
data	B-General_Concept
is	O
usually	O
provided	O
by	O
a	O
"	O
database	B-Application
management	I-Application
system	I-Application
"	O
(	O
DBMS	B-General_Concept
)	O
consisting	O
of	O
an	O
integrated	O
set	O
of	O
computer	O
software	O
that	O
allows	O
users	O
to	O
interact	O
with	O
one	O
or	O
more	O
databases	B-Application
and	O
provides	O
access	O
to	O
all	O
of	O
the	O
data	B-General_Concept
contained	O
in	O
the	O
database	O
(	O
although	O
restrictions	O
may	O
exist	O
that	O
limit	O
access	O
to	O
particular	O
data	B-General_Concept
)	O
.	O
</s>
<s>
The	O
DBMS	B-General_Concept
provides	O
various	O
functions	O
that	O
allow	O
entry	O
,	O
storage	O
and	O
retrieval	B-Library
of	O
large	O
quantities	O
of	O
information	O
and	O
provides	O
ways	O
to	O
manage	O
how	O
that	O
information	O
is	O
organized	O
.	O
</s>
<s>
Because	O
of	O
the	O
close	O
relationship	O
between	O
them	O
,	O
the	O
term	O
"	O
database	O
"	O
is	O
often	O
used	O
casually	O
to	O
refer	O
to	O
both	O
a	O
database	O
and	O
the	O
DBMS	B-General_Concept
used	O
to	O
manipulate	O
it	O
.	O
</s>
<s>
Outside	O
the	O
world	O
of	O
professional	O
information	B-General_Concept
technology	I-General_Concept
,	O
the	O
term	O
database	O
is	O
often	O
used	O
to	O
refer	O
to	O
any	O
collection	O
of	O
related	O
data	B-General_Concept
(	O
such	O
as	O
a	O
spreadsheet	B-Application
or	O
a	O
card	O
index	O
)	O
as	O
size	O
and	O
usage	O
requirements	O
typically	O
necessitate	O
use	O
of	O
a	O
database	B-Application
management	I-Application
system	I-Application
.	O
</s>
<s>
Existing	O
DBMSs	O
provide	O
various	O
functions	O
that	O
allow	O
management	O
of	O
a	O
database	O
and	O
its	O
data	B-General_Concept
which	O
can	O
be	O
classified	O
into	O
four	O
main	O
functional	O
groups	O
:	O
</s>
<s>
Data	B-Language
definition	I-Language
–	O
Creation	O
,	O
modification	O
and	O
removal	O
of	O
definitions	O
that	O
define	O
the	O
organization	O
of	O
the	O
data	B-General_Concept
.	O
</s>
<s>
Update	O
–	O
Insertion	O
,	O
modification	O
,	O
and	O
deletion	O
of	O
the	O
actual	O
data	B-General_Concept
.	O
</s>
<s>
Retrieval	B-Library
–	O
Providing	O
information	O
in	O
a	O
form	O
directly	O
usable	O
or	O
for	O
further	O
processing	O
by	O
other	O
applications	O
.	O
</s>
<s>
The	O
retrieved	O
data	B-General_Concept
may	O
be	O
made	O
available	O
in	O
a	O
form	O
basically	O
the	O
same	O
as	O
it	O
is	O
stored	O
in	O
the	O
database	O
or	O
in	O
a	O
new	O
form	O
obtained	O
by	O
altering	O
or	O
combining	O
existing	O
data	B-General_Concept
from	O
the	O
database	O
.	O
</s>
<s>
Administration	O
–	O
Registering	O
and	O
monitoring	O
users	O
,	O
enforcing	O
data	B-General_Concept
security	I-General_Concept
,	O
monitoring	O
performance	O
,	O
maintaining	O
data	B-General_Concept
integrity	O
,	O
dealing	O
with	O
concurrency	B-Operating_System
control	I-Operating_System
,	O
and	O
recovering	O
information	O
that	O
has	O
been	O
corrupted	O
by	O
some	O
event	O
such	O
as	O
an	O
unexpected	O
system	O
failure	O
.	O
</s>
<s>
Both	O
a	O
database	O
and	O
its	O
DBMS	B-General_Concept
conform	O
to	O
the	O
principles	O
of	O
a	O
particular	O
database	B-General_Concept
model	I-General_Concept
.	O
</s>
<s>
"	O
Database	B-Application
system	I-Application
"	O
refers	O
collectively	O
to	O
the	O
database	B-General_Concept
model	I-General_Concept
,	O
database	B-Application
management	I-Application
system	I-Application
,	O
and	O
database	O
.	O
</s>
<s>
Physically	O
,	O
database	O
servers	B-Application
are	O
dedicated	O
computers	O
that	O
hold	O
the	O
actual	O
databases	B-Application
and	O
run	O
only	O
the	O
DBMS	B-General_Concept
and	O
related	O
software	O
.	O
</s>
<s>
Database	O
servers	B-Application
are	O
usually	O
multiprocessor	B-Operating_System
computers	O
,	O
with	O
generous	O
memory	O
and	O
RAID	B-Architecture
disk	O
arrays	B-Data_Structure
used	O
for	O
stable	O
storage	O
.	O
</s>
<s>
Hardware	B-Architecture
database	O
accelerators	O
,	O
connected	O
to	O
one	O
or	O
more	O
servers	B-Application
via	O
a	O
high-speed	O
channel	O
,	O
are	O
also	O
used	O
in	O
large	O
volume	O
transaction	B-Application
processing	I-Application
environments	I-Application
.	O
</s>
<s>
DBMSs	O
are	O
found	O
at	O
the	O
heart	O
of	O
most	O
database	B-Application
applications	I-Application
.	O
</s>
<s>
DBMSs	O
may	O
be	O
built	O
around	O
a	O
custom	O
multitasking	B-Operating_System
kernel	B-Operating_System
with	O
built-in	O
networking	B-Architecture
support	O
,	O
but	O
modern	O
DBMSs	O
typically	O
rely	O
on	O
a	O
standard	O
operating	B-General_Concept
system	I-General_Concept
to	O
provide	O
these	O
functions	O
.	O
</s>
<s>
Since	O
DBMSs	O
comprise	O
a	O
significant	O
market	O
,	O
computer	O
and	O
storage	O
vendors	O
often	O
take	O
into	O
account	O
DBMS	B-General_Concept
requirements	O
in	O
their	O
own	O
development	O
plans	O
.	O
</s>
<s>
Databases	B-Application
and	O
DBMSs	O
can	O
be	O
categorized	O
according	O
to	O
the	O
database	O
model(s )	O
that	O
they	O
support	O
(	O
such	O
as	O
relational	B-Architecture
or	O
XML	B-Protocol
)	O
,	O
the	O
type(s )	O
of	O
computer	O
they	O
run	O
on	O
(	O
from	O
a	O
server	B-Architecture
cluster	I-Architecture
to	O
a	O
mobile	O
phone	O
)	O
,	O
the	O
query	O
language(s )	O
used	O
to	O
access	O
the	O
database	O
(	O
such	O
as	O
SQL	B-Language
or	O
XQuery	B-Language
)	O
,	O
and	O
their	O
internal	O
engineering	O
,	O
which	O
affects	O
performance	O
,	O
scalability	B-Architecture
,	O
resilience	O
,	O
and	O
security	O
.	O
</s>
<s>
The	O
sizes	O
,	O
capabilities	O
,	O
and	O
performance	O
of	O
databases	B-Application
and	O
their	O
respective	O
DBMSs	O
have	O
grown	O
in	O
orders	O
of	O
magnitude	O
.	O
</s>
<s>
These	O
performance	O
increases	O
were	O
enabled	O
by	O
the	O
technology	O
progress	O
in	O
the	O
areas	O
of	O
processors	B-General_Concept
,	O
computer	B-General_Concept
memory	I-General_Concept
,	O
computer	B-General_Concept
storage	I-General_Concept
,	O
and	O
computer	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
The	O
concept	O
of	O
a	O
database	O
was	O
made	O
possible	O
by	O
the	O
emergence	O
of	O
direct	O
access	O
storage	O
media	O
such	O
as	O
magnetic	O
disks	O
,	O
which	O
became	O
widely	O
available	O
in	O
the	O
mid-1960s	O
;	O
earlier	O
systems	O
relied	O
on	O
sequential	O
storage	O
of	O
data	B-General_Concept
on	O
magnetic	O
tape	O
.	O
</s>
<s>
The	O
subsequent	O
development	O
of	O
database	O
technology	O
can	O
be	O
divided	O
into	O
three	O
eras	O
based	O
on	O
data	B-Application
model	I-Application
or	O
structure	O
:	O
navigational	B-General_Concept
,	O
SQL/relational	O
,	O
and	O
post-relational	O
.	O
</s>
<s>
The	O
two	O
main	O
early	O
navigational	B-General_Concept
data	B-Application
models	I-Application
were	O
the	O
hierarchical	B-General_Concept
model	I-General_Concept
and	O
the	O
CODASYL	B-Language
model	O
(	O
network	B-General_Concept
model	I-General_Concept
)	O
.	O
</s>
<s>
The	O
relational	B-Architecture
model	I-Architecture
,	O
first	O
proposed	O
in	O
1970	O
by	O
Edgar	O
F	O
.	O
Codd	O
,	O
departed	O
from	O
this	O
tradition	O
by	O
insisting	O
that	O
applications	O
should	O
search	O
for	O
data	B-General_Concept
by	O
content	O
,	O
rather	O
than	O
by	O
following	O
links	O
.	O
</s>
<s>
The	O
relational	B-Architecture
model	I-Architecture
employs	O
sets	O
of	O
ledger-style	O
tables	B-Application
,	O
each	O
used	O
for	O
a	O
different	O
type	O
of	O
entity	O
.	O
</s>
<s>
Only	O
in	O
the	O
mid-1980s	O
did	O
computing	B-Architecture
hardware	I-Architecture
become	O
powerful	O
enough	O
to	O
allow	O
the	O
wide	O
deployment	O
of	O
relational	B-Architecture
systems	O
(	O
DBMSs	O
plus	O
applications	O
)	O
.	O
</s>
<s>
By	O
the	O
early	O
1990s	O
,	O
however	O
,	O
relational	B-Architecture
systems	O
dominated	O
in	O
all	O
large-scale	O
data	B-General_Concept
processing	I-General_Concept
applications	O
,	O
and	O
they	O
remain	O
dominant	O
:	O
IBM	B-Application
Db2	I-Application
,	O
Oracle	B-General_Concept
,	O
MySQL	B-Application
,	O
and	O
Microsoft	B-Application
SQL	I-Application
Server	I-Application
are	O
the	O
most	O
searched	O
DBMS	B-General_Concept
.	O
</s>
<s>
The	O
dominant	O
database	O
language	O
,	O
standardized	O
SQL	B-Language
for	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
has	O
influenced	O
database	O
languages	O
for	O
other	O
data	B-Application
models	I-Application
.	O
</s>
<s>
Object	B-Application
databases	I-Application
were	O
developed	O
in	O
the	O
1980s	O
to	O
overcome	O
the	O
inconvenience	O
of	O
object	B-Architecture
–	I-Architecture
relational	I-Architecture
impedance	I-Architecture
mismatch	I-Architecture
,	O
which	O
led	O
to	O
the	O
coining	O
of	O
the	O
term	O
"	O
post-relational	O
"	O
and	O
also	O
the	O
development	O
of	O
hybrid	O
object	B-General_Concept
–	I-General_Concept
relational	I-General_Concept
databases	I-General_Concept
.	O
</s>
<s>
The	O
next	O
generation	O
of	O
post-relational	B-General_Concept
databases	I-General_Concept
in	O
the	O
late	O
2000s	O
became	O
known	O
as	O
NoSQL	B-General_Concept
databases	B-Application
,	O
introducing	O
fast	O
key	B-Data_Structure
–	I-Data_Structure
value	I-Data_Structure
stores	I-Data_Structure
and	O
document-oriented	B-General_Concept
databases	I-General_Concept
.	O
</s>
<s>
A	O
competing	O
"	O
next	O
generation	O
"	O
known	O
as	O
NewSQL	B-General_Concept
databases	B-Application
attempted	O
new	O
implementations	O
that	O
retained	O
the	O
relational/SQL	O
model	O
while	O
aiming	O
to	O
match	O
the	O
high	O
performance	O
of	O
NoSQL	B-General_Concept
compared	O
to	O
commercially	O
available	O
relational	B-Architecture
DBMSs	O
.	O
</s>
<s>
The	O
term	O
represented	O
a	O
contrast	O
with	O
the	O
tape-based	O
systems	O
of	O
the	O
past	O
,	O
allowing	O
shared	O
interactive	O
use	O
rather	O
than	O
daily	O
batch	B-General_Concept
processing	I-General_Concept
.	O
</s>
<s>
The	B-Application
Oxford	I-Application
English	I-Application
Dictionary	I-Application
cites	O
a	O
1962	O
report	O
by	O
the	O
System	O
Development	O
Corporation	O
of	O
California	O
as	O
the	O
first	O
to	O
use	O
the	O
term	O
"	O
data-base	B-Application
"	O
in	O
a	O
specific	O
technical	O
sense	O
.	O
</s>
<s>
As	O
computers	O
grew	O
in	O
speed	O
and	O
capability	O
,	O
a	O
number	O
of	O
general-purpose	O
database	B-Application
systems	I-Application
emerged	O
;	O
by	O
the	O
mid-1960s	O
a	O
number	O
of	O
such	O
systems	O
had	O
come	O
into	O
commercial	O
use	O
.	O
</s>
<s>
Interest	O
in	O
a	O
standard	O
began	O
to	O
grow	O
,	O
and	O
Charles	O
Bachman	O
,	O
author	O
of	O
one	O
such	O
product	O
,	O
the	O
Integrated	B-Application
Data	I-Application
Store	I-Application
(	O
IDS	O
)	O
,	O
founded	O
the	O
Database	O
Task	O
Group	O
within	O
CODASYL	B-Language
,	O
the	O
group	O
responsible	O
for	O
the	O
creation	O
and	O
standardization	O
of	O
COBOL	B-Application
.	O
</s>
<s>
In	O
1971	O
,	O
the	O
Database	O
Task	O
Group	O
delivered	O
their	O
standard	O
,	O
which	O
generally	O
became	O
known	O
as	O
the	O
CODASYL	B-Language
approach	O
,	O
and	O
soon	O
a	O
number	O
of	O
commercial	O
products	O
based	O
on	O
this	O
approach	O
entered	O
the	O
market	O
.	O
</s>
<s>
The	O
CODASYL	B-Language
approach	O
offered	O
applications	O
the	O
ability	O
to	O
navigate	O
around	O
a	O
linked	O
data	B-General_Concept
set	O
which	O
was	O
formed	O
into	O
a	O
large	O
network	O
.	O
</s>
<s>
Later	O
systems	O
added	O
B-trees	B-Architecture
to	O
provide	O
alternate	O
access	O
paths	O
.	O
</s>
<s>
Many	O
CODASYL	B-Language
databases	B-Application
also	O
added	O
a	O
declarative	O
query	B-Language
language	I-Language
for	O
end	O
users	O
(	O
as	O
distinct	O
from	O
the	O
navigational	B-General_Concept
API	B-Application
)	O
.	O
</s>
<s>
However	O
,	O
CODASYL	B-Language
databases	B-Application
were	O
complex	O
and	O
required	O
significant	O
training	O
and	O
effort	O
to	O
produce	O
useful	O
applications	O
.	O
</s>
<s>
IBM	O
also	O
had	O
its	O
own	O
DBMS	B-General_Concept
in	O
1966	O
,	O
known	O
as	O
Information	B-Application
Management	I-Application
System	I-Application
(	O
IMS	O
)	O
.	O
</s>
<s>
IMS	O
was	O
a	O
development	O
of	O
software	O
written	O
for	O
the	O
Apollo	O
program	O
on	O
the	O
System/360	B-Application
.	O
</s>
<s>
IMS	O
was	O
generally	O
similar	O
in	O
concept	O
to	O
CODASYL	B-Language
,	O
but	O
used	O
a	O
strict	O
hierarchy	O
for	O
its	O
model	O
of	O
data	B-General_Concept
navigation	O
instead	O
of	O
CODASYL	B-Language
's	O
network	B-General_Concept
model	I-General_Concept
.	O
</s>
<s>
Both	O
concepts	O
later	O
became	O
known	O
as	O
navigational	B-General_Concept
databases	I-General_Concept
due	O
to	O
the	O
way	O
data	B-General_Concept
was	O
accessed	O
:	O
the	O
term	O
was	O
popularized	O
by	O
Bachman	O
's	O
1973	O
Turing	O
Award	O
presentation	O
The	O
Programmer	B-Application
as	O
Navigator	O
.	O
</s>
<s>
IMS	O
is	O
classified	O
by	O
IBM	O
as	O
a	O
hierarchical	B-General_Concept
database	I-General_Concept
.	O
</s>
<s>
IDMS	O
and	O
Cincom	B-Application
Systems	I-Application
 '	O
TOTAL	O
databases	B-Application
are	O
classified	O
as	O
network	B-General_Concept
databases	I-General_Concept
.	O
</s>
<s>
Edgar	O
F	O
.	O
Codd	O
worked	O
at	O
IBM	O
in	O
San	O
Jose	O
,	O
California	O
,	O
in	O
one	O
of	O
their	O
offshoot	O
offices	O
that	O
were	O
primarily	O
involved	O
in	O
the	O
development	O
of	O
hard	B-Device
disk	I-Device
systems	O
.	O
</s>
<s>
He	O
was	O
unhappy	O
with	O
the	O
navigational	B-General_Concept
model	O
of	O
the	O
CODASYL	B-Language
approach	O
,	O
notably	O
the	O
lack	O
of	O
a	O
"	O
search	O
"	O
facility	O
.	O
</s>
<s>
In	O
1970	O
,	O
he	O
wrote	O
a	O
number	O
of	O
papers	O
that	O
outlined	O
a	O
new	O
approach	O
to	O
database	O
construction	O
that	O
eventually	O
culminated	O
in	O
the	O
groundbreaking	O
A	O
Relational	B-Architecture
Model	I-Architecture
of	O
Data	B-General_Concept
for	O
Large	O
Shared	B-Operating_System
Data	I-Operating_System
Banks	O
.	O
</s>
<s>
In	O
this	O
paper	O
,	O
he	O
described	O
a	O
new	O
system	O
for	O
storing	O
and	O
working	O
with	O
large	O
databases	B-Application
.	O
</s>
<s>
Instead	O
of	O
records	O
being	O
stored	O
in	O
some	O
sort	O
of	O
linked	B-Data_Structure
list	I-Data_Structure
of	O
free-form	O
records	O
as	O
in	O
CODASYL	B-Language
,	O
Codd	O
's	O
idea	O
was	O
to	O
organize	O
the	O
data	B-General_Concept
as	O
a	O
number	O
of	O
"	O
tables	B-Application
"	O
,	O
each	O
table	O
being	O
used	O
for	O
a	O
different	O
type	O
of	O
entity	O
.	O
</s>
<s>
Each	O
table	O
would	O
contain	O
a	O
fixed	O
number	O
of	O
columns	B-Application
containing	O
the	O
attributes	B-Language
of	O
the	O
entity	O
.	O
</s>
<s>
One	O
or	O
more	O
columns	B-Application
of	O
each	O
table	O
were	O
designated	O
as	O
a	O
primary	B-Application
key	I-Application
by	O
which	O
the	O
rows	B-Application
of	O
the	O
table	O
could	O
be	O
uniquely	O
identified	O
;	O
cross-references	O
between	O
tables	B-Application
always	O
used	O
these	O
primary	B-Application
keys	I-Application
,	O
rather	O
than	O
disk	O
addresses	O
,	O
and	O
queries	B-Library
would	O
join	O
tables	B-Application
based	O
on	O
these	O
key	O
relationships	O
,	O
using	O
a	O
set	O
of	O
operations	O
based	O
on	O
the	O
mathematical	O
system	O
of	O
relational	B-Application
calculus	I-Application
(	O
from	O
which	O
the	O
model	O
takes	O
its	O
name	O
)	O
.	O
</s>
<s>
Splitting	O
the	O
data	B-General_Concept
into	O
a	O
set	O
of	O
normalized	O
tables	B-Application
(	O
or	O
relations	O
)	O
aimed	O
to	O
ensure	O
that	O
each	O
"	O
fact	O
"	O
was	O
only	O
stored	O
once	O
,	O
thus	O
simplifying	O
update	O
operations	O
.	O
</s>
<s>
Virtual	O
tables	B-Application
called	O
views	O
could	O
present	O
the	O
data	B-General_Concept
in	O
different	O
ways	O
for	O
different	O
users	O
,	O
but	O
views	O
could	O
not	O
be	O
directly	O
updated	O
.	O
</s>
<s>
Codd	O
used	O
mathematical	O
terms	O
to	O
define	O
the	O
model	O
:	O
relations	O
,	O
tuples	B-Application
,	O
and	O
domains	O
rather	O
than	O
tables	B-Application
,	O
rows	B-Application
,	O
and	O
columns	B-Application
.	O
</s>
<s>
The	O
use	O
of	O
primary	B-Application
keys	I-Application
(	O
user-oriented	O
identifiers	O
)	O
to	O
represent	O
cross-table	O
relationships	O
,	O
rather	O
than	O
disk	O
addresses	O
,	O
had	O
two	O
primary	O
motivations	O
.	O
</s>
<s>
From	O
an	O
engineering	O
perspective	O
,	O
it	O
enabled	O
tables	B-Application
to	O
be	O
relocated	O
and	O
resized	O
without	O
expensive	O
database	O
reorganization	O
.	O
</s>
<s>
But	O
Codd	O
was	O
more	O
interested	O
in	O
the	O
difference	O
in	O
semantics	O
:	O
the	O
use	O
of	O
explicit	O
identifiers	O
made	O
it	O
easier	O
to	O
define	O
update	O
operations	O
with	O
clean	O
mathematical	O
definitions	O
,	O
and	O
it	O
also	O
enabled	O
query	B-Library
operations	O
to	O
be	O
defined	O
in	O
terms	O
of	O
the	O
established	O
discipline	O
of	O
first-order	O
predicate	O
calculus	O
;	O
because	O
these	O
operations	O
have	O
clean	O
mathematical	O
properties	O
,	O
it	O
becomes	O
possible	O
to	O
rewrite	O
queries	B-Library
in	O
provably	O
correct	O
ways	O
,	O
which	O
is	O
the	O
basis	O
of	O
query	B-Language
optimization	I-Language
.	O
</s>
<s>
There	O
is	O
no	O
loss	O
of	O
expressiveness	O
compared	O
with	O
the	O
hierarchic	O
or	O
network	B-General_Concept
models	I-General_Concept
,	O
though	O
the	O
connections	O
between	O
tables	B-Application
are	O
no	O
longer	O
so	O
explicit	O
.	O
</s>
<s>
In	O
the	O
hierarchic	O
and	O
network	B-General_Concept
models	I-General_Concept
,	O
records	O
were	O
allowed	O
to	O
have	O
a	O
complex	O
internal	O
structure	O
.	O
</s>
<s>
In	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
the	O
process	O
of	O
normalization	B-Application
led	O
to	O
such	O
internal	O
structures	O
being	O
replaced	O
by	O
data	B-General_Concept
held	O
in	O
multiple	O
tables	B-Application
,	O
connected	O
only	O
by	O
logical	O
keys	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
common	O
use	O
of	O
a	O
database	B-Application
system	I-Application
is	O
to	O
track	O
information	O
about	O
users	O
,	O
their	O
name	O
,	O
login	O
information	O
,	O
various	O
addresses	O
and	O
phone	O
numbers	O
.	O
</s>
<s>
In	O
the	O
navigational	B-General_Concept
approach	O
,	O
all	O
of	O
this	O
data	B-General_Concept
would	O
be	O
placed	O
in	O
a	O
single	O
variable-length	O
record	O
.	O
</s>
<s>
In	O
the	O
relational	B-Architecture
approach	O
,	O
the	O
data	B-General_Concept
would	O
be	O
normalized	O
into	O
a	O
user	O
table	O
,	O
an	O
address	O
table	O
and	O
a	O
phone	O
number	O
table	O
(	O
for	O
instance	O
)	O
.	O
</s>
<s>
Records	O
would	O
be	O
created	O
in	O
these	O
optional	O
tables	B-Application
only	O
if	O
the	O
address	O
or	O
phone	O
numbers	O
were	O
actually	O
provided	O
.	O
</s>
<s>
As	O
well	O
as	O
identifying	O
rows/records	O
using	O
logical	O
identifiers	O
rather	O
than	O
disk	O
addresses	O
,	O
Codd	O
changed	O
the	O
way	O
in	O
which	O
applications	O
assembled	O
data	B-General_Concept
from	O
multiple	O
records	O
.	O
</s>
<s>
Rather	O
than	O
requiring	O
applications	O
to	O
gather	O
data	B-General_Concept
one	O
record	O
at	O
a	O
time	O
by	O
navigating	O
the	O
links	O
,	O
they	O
would	O
use	O
a	O
declarative	O
query	B-Language
language	I-Language
that	O
expressed	O
what	O
data	B-General_Concept
was	O
required	O
,	O
rather	O
than	O
the	O
access	O
path	O
by	O
which	O
it	O
should	O
be	O
found	O
.	O
</s>
<s>
Finding	O
an	O
efficient	O
access	O
path	O
to	O
the	O
data	B-General_Concept
became	O
the	O
responsibility	O
of	O
the	O
database	B-Application
management	I-Application
system	I-Application
,	O
rather	O
than	O
the	O
application	O
programmer	B-Application
.	O
</s>
<s>
This	O
process	O
,	O
called	O
query	B-Language
optimization	I-Language
,	O
depended	O
on	O
the	O
fact	O
that	O
queries	B-Library
were	O
expressed	O
in	O
terms	O
of	O
mathematical	O
logic	O
.	O
</s>
<s>
They	O
started	O
a	O
project	O
known	O
as	O
INGRES	B-Application
using	O
funding	O
that	O
had	O
already	O
been	O
allocated	O
for	O
a	O
geographical	O
database	O
project	O
and	O
student	O
programmers	B-Application
to	O
produce	O
code	B-General_Concept
.	O
</s>
<s>
Beginning	O
in	O
1973	O
,	O
INGRES	B-Application
delivered	O
its	O
first	O
test	O
products	O
which	O
were	O
generally	O
ready	O
for	O
widespread	O
use	O
in	O
1979	O
.	O
</s>
<s>
INGRES	B-Application
was	O
similar	O
to	O
System	B-Application
R	I-Application
in	O
a	O
number	O
of	O
ways	O
,	O
including	O
the	O
use	O
of	O
a	O
"	O
language	O
"	O
for	O
data	B-General_Concept
access	I-General_Concept
,	O
known	O
as	O
QUEL	B-Language
.	O
</s>
<s>
Over	O
time	O
,	O
INGRES	B-Application
moved	O
to	O
the	O
emerging	O
SQL	B-Language
standard	O
.	O
</s>
<s>
IBM	O
itself	O
did	O
one	O
test	O
implementation	O
of	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
PRTV	B-Application
,	O
and	O
a	O
production	O
one	O
,	O
Business	B-Application
System	I-Application
12	I-Application
,	O
both	O
now	O
discontinued	O
.	O
</s>
<s>
Honeywell	O
wrote	O
MRDS	B-Application
for	O
Multics	B-Application
,	O
and	O
now	O
there	O
are	O
two	O
new	O
implementations	O
:	O
Alphora	O
Dataphor	O
and	O
Rel	B-Application
.	O
</s>
<s>
Most	O
other	O
DBMS	B-General_Concept
implementations	O
usually	O
called	O
relational	B-Architecture
are	O
actually	O
SQL	B-Language
DBMSs	O
.	O
</s>
<s>
In	O
1970	O
,	O
the	O
University	O
of	O
Michigan	O
began	O
development	O
of	O
the	O
MICRO	B-Application
Information	I-Application
Management	I-Application
System	I-Application
based	O
on	O
D.L.	O
</s>
<s>
Childs	O
 '	O
Set-Theoretic	O
Data	B-Application
model	I-Application
.	O
</s>
<s>
MICRO	O
was	O
used	O
to	O
manage	O
very	O
large	O
data	B-General_Concept
sets	O
by	O
the	O
US	O
Department	O
of	O
Labor	O
,	O
the	O
U.S.	O
Environmental	O
Protection	O
Agency	O
,	O
and	O
researchers	O
from	O
the	O
University	O
of	O
Alberta	O
,	O
the	O
University	O
of	O
Michigan	O
,	O
and	O
Wayne	O
State	O
University	O
.	O
</s>
<s>
It	O
ran	O
on	O
IBM	O
mainframe	O
computers	O
using	O
the	O
Michigan	B-Application
Terminal	I-Application
System	I-Application
.	O
</s>
<s>
In	O
the	O
1970s	O
and	O
1980s	O
,	O
attempts	O
were	O
made	O
to	O
build	O
database	B-Application
systems	I-Application
with	O
integrated	O
hardware	B-Architecture
and	O
software	O
.	O
</s>
<s>
Examples	O
were	O
IBM	B-Device
System/38	I-Device
,	O
the	O
early	O
offering	O
of	O
Teradata	O
,	O
and	O
the	O
Britton	O
Lee	O
,	O
Inc	O
.	O
database	O
machine	O
.	O
</s>
<s>
Another	O
approach	O
to	O
hardware	B-Architecture
support	O
for	O
database	B-Application
management	I-Application
was	O
ICL	O
's	O
CAFS	B-Device
accelerator	O
,	O
a	O
hardware	B-Architecture
disk	O
controller	O
with	O
programmable	O
search	O
capabilities	O
.	O
</s>
<s>
Thus	O
most	O
database	B-Application
systems	I-Application
nowadays	O
are	O
software	O
systems	O
running	O
on	O
general-purpose	O
hardware	B-Architecture
,	O
using	O
general-purpose	O
computer	B-General_Concept
data	I-General_Concept
storage	I-General_Concept
.	O
</s>
<s>
However	O
,	O
this	O
idea	O
is	O
still	O
pursued	O
in	O
certain	O
applications	O
by	O
some	O
companies	O
like	O
Netezza	O
and	O
Oracle	B-General_Concept
(	O
Exadata	B-Device
)	O
.	O
</s>
<s>
IBM	O
started	O
working	O
on	O
a	O
prototype	B-Application
system	O
loosely	O
based	O
on	O
Codd	O
's	O
concepts	O
as	O
System	B-Application
R	I-Application
in	O
the	O
early	O
1970s	O
.	O
</s>
<s>
The	O
first	O
version	O
was	O
ready	O
in	O
1974/5	O
,	O
and	O
work	O
then	O
started	O
on	O
multi-table	O
systems	O
in	O
which	O
the	O
data	B-General_Concept
could	O
be	O
split	O
so	O
that	O
all	O
of	O
the	O
data	B-General_Concept
for	O
a	O
record	O
(	O
some	O
of	O
which	O
is	O
optional	O
)	O
did	O
not	O
have	O
to	O
be	O
stored	O
in	O
a	O
single	O
large	O
"	O
chunk	O
"	O
.	O
</s>
<s>
Subsequent	O
multi-user	O
versions	O
were	O
tested	O
by	O
customers	O
in	O
1978	O
and	O
1979	O
,	O
by	O
which	O
time	O
a	O
standardized	O
query	B-Language
language	I-Language
–	O
SQL	B-Language
–	O
had	O
been	O
added	O
.	O
</s>
<s>
Codd	O
's	O
ideas	O
were	O
establishing	O
themselves	O
as	O
both	O
workable	O
and	O
superior	O
to	O
CODASYL	B-Language
,	O
pushing	O
IBM	O
to	O
develop	O
a	O
true	O
production	O
version	O
of	O
System	B-Application
R	I-Application
,	O
known	O
as	O
SQL/DS	O
,	O
and	O
,	O
later	O
,	O
Database	B-Application
2	I-Application
(	O
IBM	B-Application
Db2	I-Application
)	O
.	O
</s>
<s>
Larry	O
Ellison	O
's	O
Oracle	B-General_Concept
Database	I-General_Concept
(	O
or	O
more	O
simply	O
,	O
Oracle	B-General_Concept
)	O
started	O
from	O
a	O
different	O
chain	O
,	O
based	O
on	O
IBM	O
's	O
papers	O
on	O
System	B-Application
R	I-Application
.	O
Though	O
Oracle	B-General_Concept
V1	O
implementations	O
were	O
completed	O
in	O
1978	O
,	O
it	O
was	O
not	O
until	O
Oracle	B-General_Concept
Version	O
2	O
when	O
Ellison	O
beat	O
IBM	O
to	O
market	O
in	O
1979	O
.	O
</s>
<s>
Stonebraker	O
went	O
on	O
to	O
apply	O
the	O
lessons	O
from	O
INGRES	B-Application
to	O
develop	O
a	O
new	O
database	O
,	O
Postgres	B-Application
,	O
which	O
is	O
now	O
known	O
as	O
PostgreSQL	B-Application
.	O
</s>
<s>
PostgreSQL	B-Application
is	O
often	O
used	O
for	O
global	O
mission-critical	O
applications	O
(	O
the	O
.org	O
and	O
.info	O
domain	O
name	O
registries	O
use	O
it	O
as	O
their	O
primary	O
data	B-General_Concept
store	I-General_Concept
,	O
as	O
do	O
many	O
large	O
companies	O
and	O
financial	O
institutions	O
)	O
.	O
</s>
<s>
In	O
Sweden	O
,	O
Codd	O
's	O
paper	O
was	O
also	O
read	O
and	O
Mimer	B-Application
SQL	I-Application
was	O
developed	O
in	O
the	O
mid-1970s	O
at	O
Uppsala	O
University	O
.	O
</s>
<s>
Another	O
data	B-Application
model	I-Application
,	O
the	O
entity	B-Architecture
–	I-Architecture
relationship	I-Architecture
model	I-Architecture
,	O
emerged	O
in	O
1976	O
and	O
gained	O
popularity	O
for	O
database	B-General_Concept
design	I-General_Concept
as	O
it	O
emphasized	O
a	O
more	O
familiar	O
description	O
than	O
the	O
earlier	O
relational	B-Architecture
model	I-Architecture
.	O
</s>
<s>
Later	O
on	O
,	O
entity	O
–	O
relationship	O
constructs	O
were	O
retrofitted	O
as	O
a	O
data	B-Application
modeling	I-Application
construct	O
for	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
and	O
the	O
difference	O
between	O
the	O
two	O
has	O
become	O
irrelevant	O
.	O
</s>
<s>
The	O
1980s	O
ushered	O
in	O
the	O
age	O
of	O
desktop	B-Device
computing	I-Device
.	O
</s>
<s>
The	O
new	O
computers	O
empowered	O
their	O
users	O
with	O
spreadsheets	B-Application
like	O
Lotus	B-Application
1-2-3	I-Application
and	O
database	O
software	O
like	O
dBASE	B-Application
.	O
</s>
<s>
The	O
dBASE	B-Application
product	O
was	O
lightweight	O
and	O
easy	O
for	O
any	O
computer	O
user	O
to	O
understand	O
out	O
of	O
the	O
box	O
.	O
</s>
<s>
C	O
.	O
Wayne	O
Ratliff	O
,	O
the	O
creator	O
of	O
dBASE	B-Application
,	O
stated	O
:	O
"	O
dBASE	B-Application
was	O
different	O
from	O
programs	O
like	O
BASIC	O
,	O
C	O
,	O
FORTRAN	O
,	O
and	O
COBOL	B-Application
in	O
that	O
a	O
lot	O
of	O
the	O
dirty	O
work	O
had	O
already	O
been	O
done	O
.	O
</s>
<s>
The	O
data	B-General_Concept
manipulation	O
is	O
done	O
by	O
dBASE	B-Application
instead	O
of	O
by	O
the	O
user	O
,	O
so	O
the	O
user	O
can	O
concentrate	O
on	O
what	O
he	O
is	O
doing	O
,	O
rather	O
than	O
having	O
to	O
mess	O
with	O
the	O
dirty	O
details	O
of	O
opening	O
,	O
reading	O
,	O
and	O
closing	O
files	O
,	O
and	O
managing	O
space	O
allocation.	O
"	O
</s>
<s>
dBASE	B-Application
was	O
one	O
of	O
the	O
top	O
selling	O
software	O
titles	O
in	O
the	O
1980s	O
and	O
early	O
1990s	O
.	O
</s>
<s>
The	O
1990s	O
,	O
along	O
with	O
a	O
rise	O
in	O
object-oriented	B-Language
programming	I-Language
,	O
saw	O
a	O
growth	O
in	O
how	O
data	B-General_Concept
in	O
various	O
databases	B-Application
were	O
handled	O
.	O
</s>
<s>
Programmers	B-Application
and	O
designers	O
began	O
to	O
treat	O
the	O
data	B-General_Concept
in	O
their	O
databases	B-Application
as	O
objects	O
.	O
</s>
<s>
That	O
is	O
to	O
say	O
that	O
if	O
a	O
person	O
's	O
data	B-General_Concept
were	O
in	O
a	O
database	O
,	O
that	O
person	O
's	O
attributes	B-Language
,	O
such	O
as	O
their	O
address	O
,	O
phone	O
number	O
,	O
and	O
age	O
,	O
were	O
now	O
considered	O
to	O
belong	O
to	O
that	O
person	O
instead	O
of	O
being	O
extraneous	O
data	B-General_Concept
.	O
</s>
<s>
This	O
allows	O
for	O
relations	O
between	O
data	B-General_Concept
to	O
be	O
related	O
to	O
objects	O
and	O
their	O
attributes	B-Language
and	O
not	O
to	O
individual	O
fields	O
.	O
</s>
<s>
The	O
term	O
"	O
object	B-Architecture
–	I-Architecture
relational	I-Architecture
impedance	I-Architecture
mismatch	I-Architecture
"	O
described	O
the	O
inconvenience	O
of	O
translating	O
between	O
programmed	O
objects	O
and	O
database	B-Application
tables	I-Application
.	O
</s>
<s>
Object	B-Application
databases	I-Application
and	O
object	B-General_Concept
–	I-General_Concept
relational	I-General_Concept
databases	I-General_Concept
attempt	O
to	O
solve	O
this	O
problem	O
by	O
providing	O
an	O
object-oriented	B-Language
language	I-Language
(	O
sometimes	O
as	O
extensions	O
to	O
SQL	B-Language
)	O
that	O
programmers	B-Application
can	O
use	O
as	O
alternative	O
to	O
purely	O
relational	B-Architecture
SQL	B-Language
.	O
</s>
<s>
On	O
the	O
programming	O
side	O
,	O
libraries	O
known	O
as	O
object	B-General_Concept
–	I-General_Concept
relational	I-General_Concept
mappings	I-General_Concept
(	O
ORMs	O
)	O
attempt	O
to	O
solve	O
the	O
same	O
problem	O
.	O
</s>
<s>
XML	B-Application
databases	I-Application
are	O
a	O
type	O
of	O
structured	O
document-oriented	B-General_Concept
database	I-General_Concept
that	O
allows	O
querying	O
based	O
on	O
XML	B-Protocol
document	I-Protocol
attributes	B-Language
.	O
</s>
<s>
XML	B-Application
databases	I-Application
are	O
mostly	O
used	O
in	O
applications	O
where	O
the	O
data	B-General_Concept
is	O
conveniently	O
viewed	O
as	O
a	O
collection	O
of	O
documents	O
,	O
with	O
a	O
structure	O
that	O
can	O
vary	O
from	O
the	O
very	O
flexible	O
to	O
the	O
highly	O
rigid	O
:	O
examples	O
include	O
scientific	O
articles	O
,	O
patents	O
,	O
tax	O
filings	O
,	O
and	O
personnel	O
records	O
.	O
</s>
<s>
NoSQL	B-General_Concept
databases	B-Application
are	O
often	O
very	O
fast	O
,	O
do	O
not	O
require	O
fixed	O
table	O
schemas	B-Application
,	O
avoid	O
join	O
operations	O
by	O
storing	O
denormalized	O
data	B-General_Concept
,	O
and	O
are	O
designed	O
to	O
scale	O
horizontally	O
.	O
</s>
<s>
In	O
recent	O
years	O
,	O
there	O
has	O
been	O
a	O
strong	O
demand	O
for	O
massively	O
distributed	B-Operating_System
databases	I-Operating_System
with	O
high	O
partition	O
tolerance	O
,	O
but	O
according	O
to	O
the	O
CAP	B-Operating_System
theorem	I-Operating_System
,	O
it	O
is	O
impossible	O
for	O
a	O
distributed	B-Architecture
system	I-Architecture
to	O
simultaneously	O
provide	O
consistency	B-General_Concept
,	O
availability	O
,	O
and	O
partition	O
tolerance	O
guarantees	O
.	O
</s>
<s>
A	O
distributed	B-Architecture
system	I-Architecture
can	O
satisfy	O
any	O
two	O
of	O
these	O
guarantees	O
at	O
the	O
same	O
time	O
,	O
but	O
not	O
all	O
three	O
.	O
</s>
<s>
For	O
that	O
reason	O
,	O
many	O
NoSQL	B-General_Concept
databases	B-Application
are	O
using	O
what	O
is	O
called	O
eventual	B-General_Concept
consistency	I-General_Concept
to	O
provide	O
both	O
availability	O
and	O
partition	O
tolerance	O
guarantees	O
with	O
a	O
reduced	O
level	O
of	O
data	B-General_Concept
consistency	B-General_Concept
.	O
</s>
<s>
NewSQL	B-General_Concept
is	O
a	O
class	O
of	O
modern	O
relational	B-Application
databases	I-Application
that	O
aims	O
to	O
provide	O
the	O
same	O
scalable	B-Architecture
performance	O
of	O
NoSQL	B-General_Concept
systems	O
for	O
online	O
transaction	O
processing	O
(	O
read-write	O
)	O
workloads	O
while	O
still	O
using	O
SQL	B-Language
and	O
maintaining	O
the	O
ACID	B-Operating_System
guarantees	O
of	O
a	O
traditional	O
database	B-Application
system	I-Application
.	O
</s>
<s>
Databases	B-Application
are	O
used	O
to	O
support	O
internal	O
operations	O
of	O
organizations	O
and	O
to	O
underpin	O
online	O
interactions	O
with	O
customers	O
and	O
suppliers	O
(	O
see	O
Enterprise	B-Application
software	I-Application
)	O
.	O
</s>
<s>
Databases	B-Application
are	O
used	O
to	O
hold	O
administrative	O
information	O
and	O
more	O
specialized	O
data	B-General_Concept
,	O
such	O
as	O
engineering	O
data	B-General_Concept
or	O
economic	O
models	B-Application
.	O
</s>
<s>
Examples	O
include	O
computerized	O
library	O
systems	O
,	O
flight	O
reservation	O
systems	O
,	O
computerized	O
parts	O
inventory	O
systems	O
,	O
and	O
many	O
content	B-Protocol
management	I-Protocol
systems	I-Protocol
that	O
store	O
websites	O
as	O
collections	O
of	O
webpages	O
in	O
a	O
database	O
.	O
</s>
<s>
One	O
way	O
to	O
classify	O
databases	B-Application
involves	O
the	O
type	O
of	O
their	O
contents	O
,	O
for	O
example	O
:	O
bibliographic	B-Library
,	O
document-text	O
,	O
statistical	O
,	O
or	O
multimedia	O
objects	O
.	O
</s>
<s>
This	O
section	O
lists	O
a	O
few	O
of	O
the	O
adjectives	O
used	O
to	O
characterize	O
different	O
kinds	O
of	O
databases	B-Application
.	O
</s>
<s>
An	O
in-memory	B-General_Concept
database	I-General_Concept
is	O
a	O
database	O
that	O
primarily	O
resides	O
in	O
main	O
memory	O
,	O
but	O
is	O
typically	O
backed-up	O
by	O
non-volatile	O
computer	B-General_Concept
data	I-General_Concept
storage	I-General_Concept
.	O
</s>
<s>
Main	B-General_Concept
memory	I-General_Concept
databases	I-General_Concept
are	O
faster	O
than	O
disk	O
databases	B-Application
,	O
and	O
so	O
are	O
often	O
used	O
where	O
response	O
time	O
is	O
critical	O
,	O
such	O
as	O
in	O
telecommunications	O
network	O
equipment	O
.	O
</s>
<s>
Many	O
databases	B-Application
provide	O
active	O
database	O
features	O
in	O
the	O
form	O
of	O
database	B-Language
triggers	I-Language
.	O
</s>
<s>
A	O
cloud	O
database	O
relies	O
on	O
cloud	B-Architecture
technology	I-Architecture
.	O
</s>
<s>
Both	O
the	O
database	O
and	O
most	O
of	O
its	O
DBMS	B-General_Concept
reside	O
remotely	O
,	O
"	O
in	B-Architecture
the	I-Architecture
cloud	I-Architecture
"	O
,	O
while	O
its	O
applications	O
are	O
both	O
developed	O
by	O
programmers	B-Application
and	O
later	O
maintained	O
and	O
used	O
by	O
end-users	O
through	O
a	O
web	B-Application
browser	I-Application
and	O
Open	B-Application
APIs	I-Application
.	O
</s>
<s>
Data	B-General_Concept
warehouses	O
archive	O
data	B-General_Concept
from	O
operational	O
databases	B-Application
and	O
often	O
from	O
external	O
sources	O
such	O
as	O
market	O
research	O
firms	O
.	O
</s>
<s>
The	O
warehouse	O
becomes	O
the	O
central	O
source	O
of	O
data	B-General_Concept
for	O
use	O
by	O
managers	O
and	O
other	O
end-users	O
who	O
may	O
not	O
have	O
access	O
to	O
operational	O
data	B-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
sales	O
data	B-General_Concept
might	O
be	O
aggregated	O
to	O
weekly	O
totals	O
and	O
converted	O
from	O
internal	O
product	O
codes	O
to	O
use	O
UPCs	O
so	O
that	O
they	O
can	O
be	O
compared	O
with	O
ACNielsen	O
data	B-General_Concept
.	O
</s>
<s>
Some	O
basic	O
and	O
essential	O
components	O
of	O
data	B-General_Concept
warehousing	O
include	O
extracting	O
,	O
analyzing	O
,	O
and	O
mining	B-Application
data	B-General_Concept
,	O
transforming	O
,	O
loading	O
,	O
and	O
managing	O
data	B-General_Concept
so	O
as	O
to	O
make	O
them	O
available	O
for	O
further	O
use	O
.	O
</s>
<s>
A	O
deductive	B-General_Concept
database	I-General_Concept
combines	O
logic	B-Language
programming	I-Language
with	O
a	O
relational	B-Application
database	I-Application
.	O
</s>
<s>
A	O
distributed	B-Operating_System
database	I-Operating_System
is	O
one	O
in	O
which	O
both	O
the	O
data	B-General_Concept
and	O
the	O
DBMS	B-General_Concept
span	O
multiple	O
computers	O
.	O
</s>
<s>
A	O
document-oriented	B-General_Concept
database	I-General_Concept
is	O
designed	O
for	O
storing	O
,	O
retrieving	O
,	O
and	O
managing	O
document-oriented	O
,	O
or	O
semi	O
structured	O
,	O
information	O
.	O
</s>
<s>
Document-oriented	B-General_Concept
databases	I-General_Concept
are	O
one	O
of	O
the	O
main	O
categories	O
of	O
NoSQL	B-General_Concept
databases	B-Application
.	O
</s>
<s>
An	O
embedded	B-Application
database	I-Application
system	O
is	O
a	O
DBMS	B-General_Concept
which	O
is	O
tightly	O
integrated	O
with	O
an	O
application	O
software	O
that	O
requires	O
access	O
to	O
stored	O
data	B-General_Concept
in	O
such	O
a	O
way	O
that	O
the	O
DBMS	B-General_Concept
is	O
hidden	O
from	O
the	O
application	O
's	O
end-users	O
and	O
requires	O
little	O
or	O
no	O
ongoing	O
maintenance	O
.	O
</s>
<s>
End-user	O
databases	B-Application
consist	O
of	O
data	B-General_Concept
developed	O
by	O
individual	O
end-users	O
.	O
</s>
<s>
Examples	O
of	O
these	O
are	O
collections	O
of	O
documents	O
,	O
spreadsheets	B-Application
,	O
presentations	O
,	O
multimedia	O
,	O
and	O
other	O
files	O
.	O
</s>
<s>
Several	O
products	O
exist	O
to	O
support	O
such	O
databases	B-Application
.	O
</s>
<s>
A	O
federated	B-General_Concept
database	I-General_Concept
system	I-General_Concept
comprises	O
several	O
distinct	O
databases	B-Application
,	O
each	O
with	O
its	O
own	O
DBMS	B-General_Concept
.	O
</s>
<s>
It	O
is	O
handled	O
as	O
a	O
single	O
database	O
by	O
a	O
federated	B-General_Concept
database	I-General_Concept
management	O
system	O
(	O
FDBMS	O
)	O
,	O
which	O
transparently	O
integrates	O
multiple	O
autonomous	O
DBMSs	O
,	O
possibly	O
of	O
different	O
types	O
(	O
in	O
which	O
case	O
it	O
would	O
also	O
be	O
a	O
heterogeneous	B-General_Concept
database	I-General_Concept
system	I-General_Concept
)	O
,	O
and	O
provides	O
them	O
with	O
an	O
integrated	O
conceptual	O
view	O
.	O
</s>
<s>
Sometimes	O
the	O
term	O
multi-database	O
is	O
used	O
as	O
a	O
synonym	O
for	O
federated	B-General_Concept
database	I-General_Concept
,	O
though	O
it	O
may	O
refer	O
to	O
a	O
less	O
integrated	O
(	O
e.g.	O
,	O
without	O
an	O
FDBMS	O
and	O
a	O
managed	O
integrated	O
schema	B-Application
)	O
group	O
of	O
databases	B-Application
that	O
cooperate	O
in	O
a	O
single	O
application	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
typically	O
middleware	B-General_Concept
is	O
used	O
for	O
distribution	O
,	O
which	O
typically	O
includes	O
an	O
atomic	O
commit	O
protocol	O
(	O
ACP	O
)	O
,	O
e.g.	O
,	O
the	O
two-phase	B-General_Concept
commit	I-General_Concept
protocol	I-General_Concept
,	O
to	O
allow	O
distributed	O
(	O
global	O
)	O
transactions	B-General_Concept
across	O
the	O
participating	O
databases	B-Application
.	O
</s>
<s>
A	O
graph	B-Application
database	I-Application
is	O
a	O
kind	O
of	O
NoSQL	B-General_Concept
database	O
that	O
uses	O
graph	B-Application
structures	I-Application
with	O
nodes	O
,	O
edges	O
,	O
and	O
properties	O
to	O
represent	O
and	O
store	O
information	O
.	O
</s>
<s>
General	O
graph	B-Application
databases	I-Application
that	O
can	O
store	O
any	O
graph	O
are	O
distinct	O
from	O
specialized	O
graph	B-Application
databases	I-Application
such	O
as	O
triplestores	O
and	O
network	B-General_Concept
databases	I-General_Concept
.	O
</s>
<s>
An	O
array	B-General_Concept
DBMS	I-General_Concept
is	O
a	O
kind	O
of	O
NoSQL	B-General_Concept
DBMS	B-General_Concept
that	O
allows	O
modeling	O
,	O
storage	O
,	O
and	O
retrieval	B-Library
of	O
(	O
usually	O
large	O
)	O
multi-dimensional	O
arrays	B-Data_Structure
such	O
as	O
satellite	O
images	O
and	O
climate	O
simulation	O
output	O
.	O
</s>
<s>
Hypertext	O
databases	B-Application
are	O
particularly	O
useful	O
for	O
organizing	O
large	O
amounts	O
of	O
disparate	O
information	O
.	O
</s>
<s>
A	O
knowledge	O
base	O
(	O
abbreviated	O
KB	O
,	O
kb	O
or	O
Δ	O
)	O
is	O
a	O
special	O
kind	O
of	O
database	O
for	O
knowledge	O
management	O
,	O
providing	O
the	O
means	O
for	O
the	O
computerized	O
collection	O
,	O
organization	O
,	O
and	O
retrieval	B-Library
of	O
knowledge	O
.	O
</s>
<s>
Also	O
a	O
collection	O
of	O
data	B-General_Concept
representing	O
problems	O
with	O
their	O
solutions	O
and	O
related	O
experiences	O
.	O
</s>
<s>
Operational	O
databases	B-Application
store	O
detailed	O
data	B-General_Concept
about	O
the	O
operations	O
of	O
an	O
organization	O
.	O
</s>
<s>
They	O
typically	O
process	O
relatively	O
high	O
volumes	O
of	O
updates	O
using	O
transactions	B-General_Concept
.	O
</s>
<s>
Examples	O
include	O
customer	O
databases	B-Application
that	O
record	O
contact	O
,	O
credit	O
,	O
and	O
demographic	O
information	O
about	O
a	O
business	O
's	O
customers	O
,	O
personnel	O
databases	B-Application
that	O
hold	O
information	O
such	O
as	O
salary	O
,	O
benefits	O
,	O
skills	O
data	B-General_Concept
about	O
employees	O
,	O
enterprise	O
resource	O
planning	O
systems	O
that	O
record	O
details	O
about	O
product	O
components	O
,	O
parts	O
inventory	O
,	O
and	O
financial	O
databases	B-Application
that	O
keep	O
track	O
of	O
the	O
organization	O
's	O
money	O
,	O
accounting	O
and	O
financial	O
dealings	O
.	O
</s>
<s>
A	O
parallel	O
database	O
seeks	O
to	O
improve	O
performance	O
through	O
parallelization	B-Operating_System
for	O
tasks	O
such	O
as	O
loading	O
data	B-General_Concept
,	O
building	O
indexes	B-Data_Structure
and	O
evaluating	O
queries	B-Library
.	O
</s>
<s>
The	O
major	O
parallel	O
DBMS	B-General_Concept
architectures	O
which	O
are	O
induced	O
by	O
the	O
underlying	O
hardware	B-Architecture
architecture	O
are	O
:	O
</s>
<s>
Shared	B-Operating_System
memory	I-Operating_System
architecture	I-Operating_System
,	O
where	O
multiple	O
processors	B-General_Concept
share	O
the	O
main	O
memory	O
space	O
,	O
as	O
well	O
as	O
other	O
data	B-General_Concept
storage	O
.	O
</s>
<s>
Shared	O
disk	O
architecture	O
,	O
where	O
each	O
processing	O
unit	O
(	O
typically	O
consisting	O
of	O
multiple	O
processors	B-General_Concept
)	O
has	O
its	O
own	O
main	O
memory	O
,	O
but	O
all	O
units	O
share	O
the	O
other	O
storage	O
.	O
</s>
<s>
Shared-nothing	B-Operating_System
architecture	I-Operating_System
,	O
where	O
each	O
processing	O
unit	O
has	O
its	O
own	O
main	O
memory	O
and	O
other	O
storage	O
.	O
</s>
<s>
Probabilistic	B-General_Concept
databases	I-General_Concept
employ	O
fuzzy	O
logic	O
to	O
draw	O
inferences	O
from	O
imprecise	O
data	B-General_Concept
.	O
</s>
<s>
Real-time	B-Application
databases	I-Application
process	O
transactions	B-General_Concept
fast	O
enough	O
for	O
the	O
result	O
to	O
come	O
back	O
and	O
be	O
acted	O
on	O
right	O
away	O
.	O
</s>
<s>
A	O
spatial	B-Algorithm
database	I-Algorithm
can	O
store	O
the	O
data	B-General_Concept
with	O
multidimensional	O
features	O
.	O
</s>
<s>
The	O
queries	B-Library
on	O
such	O
data	B-General_Concept
include	O
location-based	O
queries	B-Library
,	O
like	O
"	O
Where	O
is	O
the	O
closest	O
hotel	O
in	O
my	O
area	O
?	O
</s>
<s>
A	O
temporal	O
database	O
has	O
built-in	O
time	O
aspects	O
,	O
for	O
example	O
a	O
temporal	O
data	B-Application
model	I-Application
and	O
a	O
temporal	O
version	O
of	O
SQL	B-Language
.	O
</s>
<s>
A	O
terminology-oriented	B-Application
database	I-Application
builds	O
upon	O
an	O
object-oriented	B-Application
database	I-Application
,	O
often	O
customized	O
for	O
a	O
specific	O
field	O
.	O
</s>
<s>
An	O
unstructured	B-Application
data	I-Application
database	O
is	O
intended	O
to	O
store	O
in	O
a	O
manageable	O
and	O
protected	O
way	O
diverse	O
objects	O
that	O
do	O
not	O
fit	O
naturally	O
and	O
conveniently	O
in	O
common	O
databases	B-Application
.	O
</s>
<s>
Most	O
established	O
DBMSs	O
now	O
support	O
unstructured	B-Application
data	I-Application
in	O
various	O
ways	O
,	O
and	O
new	O
dedicated	O
DBMSs	O
are	O
emerging	O
.	O
</s>
<s>
Connolly	O
and	O
Begg	O
define	O
database	B-Application
management	I-Application
system	I-Application
(	O
DBMS	B-General_Concept
)	O
as	O
a	O
"	O
software	O
system	O
that	O
enables	O
users	O
to	O
define	O
,	O
create	O
,	O
maintain	O
and	O
control	O
access	O
to	O
the	O
database	O
"	O
.	O
</s>
<s>
Examples	O
of	O
DBMS	B-General_Concept
's	O
include	O
MySQL	B-Application
,	O
MariaDB	B-Application
,	O
PostgreSQL	B-Application
,	O
Microsoft	B-Application
SQL	I-Application
Server	I-Application
,	O
Oracle	B-General_Concept
Database	I-General_Concept
,	O
and	O
Microsoft	B-Application
Access	I-Application
.	O
</s>
<s>
The	O
DBMS	B-General_Concept
acronym	O
is	O
sometimes	O
extended	O
to	O
indicate	O
the	O
underlying	O
database	B-General_Concept
model	I-General_Concept
,	O
with	O
RDBMS	O
for	O
the	O
relational	B-Architecture
,	O
OODBMS	B-Application
for	O
the	O
object	O
(	O
oriented	O
)	O
and	O
ORDBMS	B-General_Concept
for	O
the	O
object	B-General_Concept
–	I-General_Concept
relational	I-General_Concept
model	I-General_Concept
.	O
</s>
<s>
Other	O
extensions	O
can	O
indicate	O
some	O
other	O
characteristics	O
,	O
such	O
as	O
DDBMS	B-Application
for	O
a	O
distributed	B-Application
database	I-Application
management	I-Application
systems	I-Application
.	O
</s>
<s>
The	O
functionality	O
provided	O
by	O
a	O
DBMS	B-General_Concept
can	O
vary	O
enormously	O
.	O
</s>
<s>
The	O
core	O
functionality	O
is	O
the	O
storage	O
,	O
retrieval	B-Library
and	O
update	O
of	O
data	B-General_Concept
.	O
</s>
<s>
Codd	O
proposed	O
the	O
following	O
functions	O
and	O
services	O
a	O
fully-fledged	O
general	O
purpose	O
DBMS	B-General_Concept
should	O
provide	O
:	O
</s>
<s>
It	O
is	O
also	O
generally	O
to	O
be	O
expected	O
the	O
DBMS	B-General_Concept
will	O
provide	O
a	O
set	O
of	O
utilities	O
for	O
such	O
purposes	O
as	O
may	O
be	O
necessary	O
to	O
administer	O
the	O
database	O
effectively	O
,	O
including	O
import	O
,	O
export	O
,	O
monitoring	O
,	O
defragmentation	O
and	O
analysis	O
utilities	O
.	O
</s>
<s>
The	O
core	O
part	O
of	O
the	O
DBMS	B-General_Concept
interacting	O
between	O
the	O
database	O
and	O
the	O
application	O
interface	O
sometimes	O
referred	O
to	O
as	O
the	O
database	B-General_Concept
engine	I-General_Concept
.	O
</s>
<s>
The	O
trend	O
is	O
to	O
minimize	O
the	O
amount	O
of	O
manual	O
configuration	O
,	O
and	O
for	O
cases	O
such	O
as	O
embedded	B-Application
databases	I-Application
the	O
need	O
to	O
target	O
zero-administration	O
is	O
paramount	O
.	O
</s>
<s>
Early	O
multi-user	O
DBMS	B-General_Concept
typically	O
only	O
allowed	O
for	O
the	O
application	O
to	O
reside	O
on	O
the	O
same	O
computer	O
with	O
access	O
via	O
terminals	B-General_Concept
or	O
terminal	O
emulation	O
software	O
.	O
</s>
<s>
The	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
architecture	I-Operating_System
was	O
a	O
development	O
where	O
the	O
application	O
resided	O
on	O
a	O
client	O
desktop	O
and	O
the	O
database	O
on	O
a	O
server	O
allowing	O
the	O
processing	O
to	O
be	O
distributed	O
.	O
</s>
<s>
This	O
evolved	O
into	O
a	O
multitier	B-Operating_System
architecture	I-Operating_System
incorporating	O
application	B-Application
servers	I-Application
and	O
web	B-Application
servers	I-Application
with	O
the	O
end	O
user	B-Application
interface	I-Application
via	O
a	O
web	B-Application
browser	I-Application
with	O
the	O
database	O
only	O
directly	O
connected	O
to	O
the	O
adjacent	O
tier	B-Operating_System
.	O
</s>
<s>
A	O
general-purpose	O
DBMS	B-General_Concept
will	O
provide	O
public	O
application	B-Application
programming	I-Application
interfaces	I-Application
(	O
API	B-Application
)	O
and	O
optionally	O
a	O
processor	O
for	O
database	O
languages	O
such	O
as	O
SQL	B-Language
to	O
allow	O
applications	O
to	O
be	O
written	O
to	O
interact	O
with	O
and	O
manipulate	O
the	O
database	O
.	O
</s>
<s>
A	O
special	O
purpose	O
DBMS	B-General_Concept
may	O
use	O
a	O
private	O
API	B-Application
and	O
be	O
specifically	O
customized	O
and	O
linked	O
to	O
a	O
single	O
application	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
email	O
system	O
performs	O
many	O
of	O
the	O
functions	O
of	O
a	O
general-purpose	O
DBMS	B-General_Concept
such	O
as	O
message	O
insertion	O
,	O
message	O
deletion	O
,	O
attachment	O
handling	O
,	O
blocklist	O
lookup	O
,	O
associating	O
messages	O
an	O
email	O
address	O
and	O
so	O
forth	O
however	O
these	O
functions	O
are	O
limited	O
to	O
what	O
is	O
required	O
to	O
handle	O
email	O
.	O
</s>
<s>
External	O
interaction	O
with	O
the	O
database	O
will	O
be	O
via	O
an	O
application	O
program	O
that	O
interfaces	O
with	O
the	O
DBMS	B-General_Concept
.	O
</s>
<s>
This	O
can	O
range	O
from	O
a	O
database	B-Application
tool	I-Application
that	O
allows	O
users	O
to	O
execute	O
SQL	B-Language
queries	B-Library
textually	O
or	O
graphically	O
,	O
to	O
a	O
website	O
that	O
happens	O
to	O
use	O
a	O
database	O
to	O
store	O
and	O
search	O
information	O
.	O
</s>
<s>
A	O
programmer	B-Application
will	O
code	B-General_Concept
interactions	O
to	O
the	O
database	O
(	O
sometimes	O
referred	O
to	O
as	O
a	O
datasource	B-General_Concept
)	O
via	O
an	O
application	B-Application
program	I-Application
interface	I-Application
(	O
API	B-Application
)	O
or	O
via	O
a	O
database	O
language	O
.	O
</s>
<s>
The	O
particular	O
API	B-Application
or	O
language	O
chosen	O
will	O
need	O
to	O
be	O
supported	O
by	O
DBMS	B-General_Concept
,	O
possibly	O
indirectly	O
via	O
a	O
preprocessor	B-General_Concept
or	O
a	O
bridging	O
API	B-Application
.	O
</s>
<s>
Some	O
API	B-Application
's	O
aim	O
to	O
be	O
database	O
independent	O
,	O
ODBC	B-Application
being	O
a	O
commonly	O
known	O
example	O
.	O
</s>
<s>
Other	O
common	O
API	B-Application
's	O
include	O
JDBC	B-Language
and	O
ADO.NET	B-Device
.	O
</s>
<s>
Database	O
languages	O
are	O
special-purpose	O
languages	O
,	O
which	O
allow	O
one	O
or	O
more	O
of	O
the	O
following	O
tasks	O
,	O
sometimes	O
distinguished	O
as	O
sublanguages	B-Application
:	O
</s>
<s>
Data	B-Application
control	I-Application
language	I-Application
(	O
DCL	O
)	O
–	O
controls	O
access	O
to	O
data	B-General_Concept
;	O
</s>
<s>
Data	B-Language
definition	I-Language
language	I-Language
(	O
DDL	O
)	O
–	O
defines	O
data	B-General_Concept
types	O
such	O
as	O
creating	O
,	O
altering	O
,	O
or	O
dropping	O
tables	B-Application
and	O
the	O
relationships	O
among	O
them	O
;	O
</s>
<s>
Data	B-Language
manipulation	I-Language
language	I-Language
(	O
DML	O
)	O
–	O
performs	O
tasks	O
such	O
as	O
inserting	O
,	O
updating	O
,	O
or	O
deleting	O
data	B-General_Concept
occurrences	O
;	O
</s>
<s>
Data	B-Application
query	I-Application
language	I-Application
(	O
DQL	O
)	O
–	O
allows	O
searching	O
for	O
information	O
and	O
computing	O
derived	O
information	O
.	O
</s>
<s>
Database	O
languages	O
are	O
specific	O
to	O
a	O
particular	O
data	B-Application
model	I-Application
.	O
</s>
<s>
SQL	B-Language
combines	O
the	O
roles	O
of	O
data	B-Language
definition	I-Language
,	O
data	B-General_Concept
manipulation	O
,	O
and	O
query	B-Library
in	O
a	O
single	O
language	O
.	O
</s>
<s>
It	O
was	O
one	O
of	O
the	O
first	O
commercial	O
languages	O
for	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
although	O
it	O
departs	O
in	O
some	O
respects	O
from	O
the	B-Application
relational	I-Application
model	I-Application
as	I-Application
described	I-Application
by	I-Application
Codd	I-Application
(	O
for	O
example	O
,	O
the	O
rows	B-Application
and	O
columns	B-Application
of	O
a	O
table	O
can	O
be	O
ordered	O
)	O
.	O
</s>
<s>
SQL	B-Language
became	O
a	O
standard	O
of	O
the	O
American	O
National	O
Standards	O
Institute	O
(	O
ANSI	O
)	O
in	O
1986	O
,	O
and	O
of	O
the	O
International	O
Organization	O
for	O
Standardization	O
(	O
ISO	O
)	O
in	O
1987	O
.	O
</s>
<s>
The	O
standards	O
have	O
been	O
regularly	O
enhanced	O
since	O
and	O
are	O
supported	O
(	O
with	O
varying	O
degrees	O
of	O
conformance	O
)	O
by	O
all	O
mainstream	O
commercial	O
relational	B-Architecture
DBMSs	O
.	O
</s>
<s>
OQL	B-Language
is	O
an	O
object	B-Application
model	I-Application
language	O
standard	O
(	O
from	O
the	O
Object	B-Application
Data	I-Application
Management	I-Application
Group	I-Application
)	O
.	O
</s>
<s>
It	O
has	O
influenced	O
the	O
design	O
of	O
some	O
of	O
the	O
newer	O
query	B-Language
languages	I-Language
like	O
JDOQL	O
and	O
EJB	B-Language
QL	I-Language
.	O
</s>
<s>
XQuery	B-Language
is	O
a	O
standard	O
XML	B-Language
query	I-Language
language	I-Language
implemented	O
by	O
XML	B-Application
database	I-Application
systems	O
such	O
as	O
MarkLogic	O
and	O
eXist	O
,	O
by	O
relational	B-Application
databases	I-Application
with	O
XML	B-Protocol
capability	O
such	O
as	O
Oracle	B-General_Concept
and	O
Db2	B-Application
,	O
and	O
also	O
by	O
in-memory	B-General_Concept
XML	B-Protocol
processors	B-General_Concept
such	O
as	O
Saxon	B-Language
.	O
</s>
<s>
SQL/XML	B-Language
combines	O
XQuery	B-Language
with	O
SQL	B-Language
.	O
</s>
<s>
Database	B-General_Concept
storage	I-General_Concept
is	O
the	O
container	O
of	O
the	O
physical	O
materialization	O
of	O
a	O
database	O
.	O
</s>
<s>
It	O
also	O
contains	O
all	O
the	O
information	O
needed	O
(	O
e.g.	O
,	O
metadata	O
,	O
"	O
data	B-General_Concept
about	O
the	O
data	B-General_Concept
"	O
,	O
and	O
internal	O
data	B-General_Concept
structures	I-General_Concept
)	O
to	O
reconstruct	O
the	O
conceptual	O
level	O
and	O
external	O
level	O
from	O
the	O
internal	O
level	O
when	O
needed	O
.	O
</s>
<s>
Databases	B-Application
as	O
digital	O
objects	O
contain	O
three	B-Operating_System
layers	I-Operating_System
of	O
information	O
which	O
must	O
be	O
stored	O
:	O
the	O
data	B-General_Concept
,	O
the	O
structure	O
,	O
and	O
the	O
semantics	O
.	O
</s>
<s>
Proper	O
storage	O
of	O
all	O
three	B-Operating_System
layers	I-Operating_System
is	O
needed	O
for	O
future	O
preservation	B-General_Concept
and	O
longevity	O
of	O
the	O
database	O
.	O
</s>
<s>
Putting	O
data	B-General_Concept
into	O
permanent	O
storage	O
is	O
generally	O
the	O
responsibility	O
of	O
the	O
database	B-General_Concept
engine	I-General_Concept
a.k.a.	O
</s>
<s>
"	O
storage	B-General_Concept
engine	I-General_Concept
"	O
.	O
</s>
<s>
Though	O
typically	O
accessed	O
by	O
a	O
DBMS	B-General_Concept
through	O
the	O
underlying	O
operating	B-General_Concept
system	I-General_Concept
(	O
and	O
often	O
using	O
the	O
operating	B-General_Concept
systems	I-General_Concept
 '	O
file	B-Application
systems	I-Application
as	O
intermediates	O
for	O
storage	O
layout	O
)	O
,	O
storage	O
properties	O
and	O
configuration	O
settings	O
are	O
extremely	O
important	O
for	O
the	O
efficient	O
operation	O
of	O
the	O
DBMS	B-General_Concept
,	O
and	O
thus	O
are	O
closely	O
maintained	O
by	O
database	O
administrators	O
.	O
</s>
<s>
A	O
DBMS	B-General_Concept
,	O
while	O
in	O
operation	O
,	O
always	O
has	O
its	O
database	O
residing	O
in	O
several	O
types	O
of	O
storage	O
(	O
e.g.	O
,	O
memory	O
and	O
external	O
storage	O
)	O
.	O
</s>
<s>
The	O
database	O
data	B-General_Concept
and	O
the	O
additional	O
needed	O
information	O
,	O
possibly	O
in	O
very	O
large	O
amounts	O
,	O
are	O
coded	O
into	O
bits	O
.	O
</s>
<s>
Data	B-General_Concept
typically	O
reside	O
in	O
the	O
storage	O
in	O
structures	O
that	O
look	O
completely	O
different	O
from	O
the	O
way	O
the	O
data	B-General_Concept
look	O
at	O
the	O
conceptual	O
and	O
external	O
levels	O
,	O
but	O
in	O
ways	O
that	O
attempt	O
to	O
optimize	O
(	O
the	O
best	O
possible	O
)	O
these	O
levels	O
 '	O
reconstruction	O
when	O
needed	O
by	O
users	O
and	O
programs	O
,	O
as	O
well	O
as	O
for	O
computing	O
additional	O
types	O
of	O
needed	O
information	O
from	O
the	O
data	B-General_Concept
(	O
e.g.	O
,	O
when	O
querying	O
the	O
database	O
)	O
.	O
</s>
<s>
Some	O
DBMSs	O
support	O
specifying	O
which	O
character	B-General_Concept
encoding	I-General_Concept
was	O
used	O
to	O
store	O
data	B-General_Concept
,	O
so	O
multiple	O
encodings	O
can	O
be	O
used	O
in	O
the	O
same	O
database	O
.	O
</s>
<s>
Various	O
low-level	O
database	B-General_Concept
storage	I-General_Concept
structures	I-General_Concept
are	O
used	O
by	O
the	O
storage	B-General_Concept
engine	I-General_Concept
to	O
serialize	O
the	O
data	B-Application
model	I-Application
so	O
it	O
can	O
be	O
written	O
to	O
the	O
medium	O
of	O
choice	O
.	O
</s>
<s>
Conventional	O
storage	O
is	O
row-oriented	O
,	O
but	O
there	O
are	O
also	O
column-oriented	B-General_Concept
and	O
correlation	O
databases	B-Application
.	O
</s>
<s>
Often	O
storage	O
redundancy	B-Application
is	O
employed	O
to	O
increase	O
performance	O
.	O
</s>
<s>
A	O
common	O
example	O
is	O
storing	O
materialized	B-Application
views	I-Application
,	O
which	O
consist	O
of	O
frequently	O
needed	O
external	O
views	O
or	O
query	B-Library
results	O
.	O
</s>
<s>
The	O
downsides	O
of	O
materialized	B-Application
views	I-Application
are	O
the	O
overhead	O
incurred	O
when	O
updating	O
them	O
to	O
keep	O
them	O
synchronized	O
with	O
their	O
original	O
updated	O
database	O
data	B-General_Concept
,	O
and	O
the	O
cost	O
of	O
storage	O
redundancy	B-Application
.	O
</s>
<s>
Occasionally	O
a	O
database	O
employs	O
storage	O
redundancy	B-Application
by	O
database	O
objects	O
replication	O
(	O
with	O
one	O
or	O
more	O
copies	O
)	O
to	O
increase	O
data	B-General_Concept
availability	O
(	O
both	O
to	O
improve	O
performance	O
of	O
simultaneous	O
multiple	O
end-user	O
accesses	O
to	O
the	O
same	O
database	O
object	O
,	O
and	O
to	O
provide	O
resiliency	O
in	O
a	O
case	O
of	O
partial	O
failure	O
of	O
a	O
distributed	B-Operating_System
database	I-Operating_System
)	O
.	O
</s>
<s>
With	O
data	B-General_Concept
virtualization	I-General_Concept
,	O
the	O
data	B-General_Concept
used	O
remains	O
in	O
its	O
original	O
locations	O
and	O
real-time	O
access	O
is	O
established	O
to	O
allow	O
analytics	O
across	O
multiple	O
sources	O
.	O
</s>
<s>
This	O
can	O
aid	O
in	O
resolving	O
some	O
technical	O
difficulties	O
such	O
as	O
compatibility	O
problems	O
when	O
combining	O
data	B-General_Concept
from	O
various	O
platforms	O
,	O
lowering	O
the	O
risk	O
of	O
error	O
caused	O
by	O
faulty	O
data	B-General_Concept
,	O
and	O
guaranteeing	O
that	O
the	O
newest	O
data	B-General_Concept
is	O
used	O
.	O
</s>
<s>
However	O
,	O
with	O
data	B-General_Concept
virtualization	I-General_Concept
,	O
the	O
connection	O
to	O
all	O
necessary	O
data	B-General_Concept
sources	O
must	O
be	O
operational	O
as	O
there	O
is	O
no	O
local	O
copy	O
of	O
the	O
data	B-General_Concept
,	O
which	O
is	O
one	O
of	O
the	O
main	O
drawbacks	O
of	O
the	O
approach	O
.	O
</s>
<s>
The	O
information	O
may	O
comprise	O
specific	O
database	O
objects	O
(	O
e.g.	O
,	O
record	O
types	O
,	O
specific	O
records	O
,	O
data	B-General_Concept
structures	I-General_Concept
)	O
,	O
certain	O
computations	O
over	O
certain	O
objects	O
(	O
e.g.	O
,	O
query	B-Library
types	O
,	O
or	O
specific	O
queries	B-Library
)	O
,	O
or	O
using	O
specific	O
access	O
paths	O
to	O
the	O
former	O
(	O
e.g.	O
,	O
using	O
specific	O
indexes	B-Data_Structure
or	O
other	O
data	B-General_Concept
structures	I-General_Concept
to	O
access	O
information	O
)	O
.	O
</s>
<s>
Database	O
access	O
controls	O
are	O
set	O
by	O
special	O
authorized	O
(	O
by	O
the	O
database	O
owner	O
)	O
personnel	O
that	O
uses	O
dedicated	O
protected	O
security	O
DBMS	B-General_Concept
interfaces	O
.	O
</s>
<s>
This	O
may	O
be	O
managed	O
directly	O
on	O
an	O
individual	O
basis	O
,	O
or	O
by	O
the	O
assignment	O
of	O
individuals	O
and	O
privileges	O
to	O
groups	O
,	O
or	O
(	O
in	O
the	O
most	O
elaborate	O
models	B-Application
)	O
through	O
the	O
assignment	O
of	O
individuals	O
and	O
groups	O
to	O
roles	O
which	O
are	O
then	O
granted	O
entitlements	O
.	O
</s>
<s>
Data	B-General_Concept
security	I-General_Concept
prevents	O
unauthorized	O
users	O
from	O
viewing	O
or	O
updating	O
the	O
database	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
employee	O
database	O
can	O
contain	O
all	O
the	O
data	B-General_Concept
about	O
an	O
individual	O
employee	O
,	O
but	O
one	O
group	O
of	O
users	O
may	O
be	O
authorized	O
to	O
view	O
only	O
payroll	O
data	B-General_Concept
,	O
while	O
others	O
are	O
allowed	O
access	O
to	O
only	O
work	O
history	O
and	O
medical	O
data	B-General_Concept
.	O
</s>
<s>
If	O
the	O
DBMS	B-General_Concept
provides	O
a	O
way	O
to	O
interactively	O
enter	O
and	O
update	O
the	O
database	O
,	O
as	O
well	O
as	O
interrogate	O
it	O
,	O
this	O
capability	O
allows	O
for	O
managing	O
personal	O
databases	B-Application
.	O
</s>
<s>
Data	B-General_Concept
security	I-General_Concept
in	O
general	O
deals	O
with	O
protecting	O
specific	O
chunks	O
of	O
data	B-General_Concept
,	O
both	O
physically	O
(	O
i.e.	O
,	O
from	O
corruption	O
,	O
or	O
destruction	O
,	O
or	O
removal	O
;	O
e.g.	O
,	O
see	O
physical	O
security	O
)	O
,	O
or	O
the	O
interpretation	O
of	O
them	O
,	O
or	O
parts	O
of	O
them	O
to	O
meaningful	O
information	O
(	O
e.g.	O
,	O
by	O
looking	O
at	O
the	O
strings	O
of	O
bits	O
that	O
they	O
comprise	O
,	O
concluding	O
specific	O
valid	O
credit-card	O
numbers	O
;	O
e.g.	O
,	O
see	O
data	B-General_Concept
encryption	O
)	O
.	O
</s>
<s>
Change	O
and	O
access	O
logging	O
records	O
who	O
accessed	O
which	O
attributes	B-Language
,	O
what	O
was	O
changed	O
,	O
and	O
when	O
it	O
was	O
changed	O
.	O
</s>
<s>
Logging	O
services	O
allow	O
for	O
a	O
forensic	B-Application
database	I-Application
audit	O
later	O
by	O
keeping	O
a	O
record	O
of	O
access	O
occurrences	O
and	O
changes	O
.	O
</s>
<s>
Sometimes	O
application-level	O
code	B-General_Concept
is	O
used	O
to	O
record	O
changes	O
rather	O
than	O
leaving	O
this	O
in	O
the	O
database	O
.	O
</s>
<s>
Database	B-General_Concept
transactions	I-General_Concept
can	O
be	O
used	O
to	O
introduce	O
some	O
level	O
of	O
fault	B-General_Concept
tolerance	I-General_Concept
and	O
data	B-General_Concept
integrity	O
after	O
recovery	O
from	O
a	O
crash	B-General_Concept
.	O
</s>
<s>
A	O
database	B-General_Concept
transaction	I-General_Concept
is	O
a	O
unit	B-General_Concept
of	I-General_Concept
work	I-General_Concept
,	O
typically	O
encapsulating	O
a	O
number	O
of	O
operations	O
over	O
a	O
database	O
(	O
e.g.	O
,	O
reading	O
a	O
database	O
object	O
,	O
writing	O
,	O
acquiring	O
or	O
releasing	O
a	O
lock	B-Operating_System
,	O
etc	O
.	O
</s>
<s>
Each	O
transaction	O
has	O
well	O
defined	O
boundaries	O
in	O
terms	O
of	O
which	O
program/code	O
executions	O
are	O
included	O
in	O
that	O
transaction	O
(	O
determined	O
by	O
the	O
transaction	O
's	O
programmer	B-Application
via	O
special	O
transaction	O
commands	O
)	O
.	O
</s>
<s>
The	O
acronym	O
ACID	B-Operating_System
describes	O
some	O
ideal	O
properties	O
of	O
a	O
database	B-General_Concept
transaction	I-General_Concept
:	O
atomicity	B-General_Concept
,	O
consistency	B-General_Concept
,	O
isolation	B-General_Concept
,	O
and	O
durability	B-General_Concept
.	O
</s>
<s>
A	O
database	O
built	O
with	O
one	O
DBMS	B-General_Concept
is	O
not	O
portable	O
to	O
another	O
DBMS	B-General_Concept
(	O
i.e.	O
,	O
the	O
other	O
DBMS	B-General_Concept
cannot	O
run	O
it	O
)	O
.	O
</s>
<s>
However	O
,	O
in	O
some	O
situations	O
,	O
it	O
is	O
desirable	O
to	O
migrate	O
a	O
database	O
from	O
one	O
DBMS	B-General_Concept
to	O
another	O
.	O
</s>
<s>
The	O
migration	O
involves	O
the	O
database	O
's	O
transformation	O
from	O
one	O
DBMS	B-General_Concept
type	O
to	O
another	O
.	O
</s>
<s>
Typically	O
,	O
a	O
DBMS	B-General_Concept
vendor	O
provides	O
tools	O
to	O
help	O
import	O
databases	B-Application
from	O
other	O
popular	O
DBMSs	O
.	O
</s>
<s>
Typically	O
,	O
an	O
appropriate	O
general-purpose	O
DBMS	B-General_Concept
can	O
be	O
selected	O
to	O
be	O
used	O
for	O
this	O
purpose	O
.	O
</s>
<s>
A	O
DBMS	B-General_Concept
provides	O
the	O
needed	O
user	B-Application
interfaces	I-Application
to	O
be	O
used	O
by	O
database	O
administrators	O
to	O
define	O
the	O
needed	O
application	O
's	O
data	B-General_Concept
structures	I-General_Concept
within	O
the	O
DBMS	B-General_Concept
's	O
respective	O
data	B-Application
model	I-Application
.	O
</s>
<s>
Other	O
user	B-Application
interfaces	I-Application
are	O
used	O
to	O
select	O
needed	O
DBMS	B-General_Concept
parameters	O
(	O
like	O
security	O
related	O
,	O
storage	O
allocation	O
parameters	O
,	O
etc	O
.	O
</s>
<s>
When	O
the	O
database	O
is	O
ready	O
(	O
all	O
its	O
data	B-General_Concept
structures	I-General_Concept
and	O
other	O
needed	O
components	O
are	O
defined	O
)	O
,	O
it	O
is	O
typically	O
populated	O
with	O
initial	O
application	O
's	O
data	B-General_Concept
(	O
database	O
initialization	O
,	O
which	O
is	O
typically	O
a	O
distinct	O
project	O
;	O
in	O
many	O
cases	O
using	O
specialized	O
DBMS	B-General_Concept
interfaces	O
that	O
support	O
bulk	O
insertion	O
)	O
before	O
making	O
it	O
operational	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
the	O
database	O
becomes	O
operational	O
while	O
empty	O
of	O
application	O
data	B-General_Concept
,	O
and	O
data	B-General_Concept
are	O
accumulated	O
during	O
its	O
operation	O
.	O
</s>
<s>
Various	O
database	O
parameters	O
may	O
need	O
changing	O
and	O
the	O
database	O
may	O
need	O
to	O
be	O
tuned	O
(	O
tuning	B-General_Concept
)	O
for	O
better	O
performance	O
;	O
application	O
's	O
data	B-General_Concept
structures	I-General_Concept
may	O
be	O
changed	O
or	O
added	O
,	O
new	O
related	O
application	O
programs	O
may	O
be	O
written	O
to	O
add	O
to	O
the	O
application	O
's	O
functionality	O
,	O
etc	O
.	O
</s>
<s>
Sometimes	O
it	O
is	O
desired	O
to	O
bring	O
a	O
database	O
back	O
to	O
a	O
previous	O
state	O
(	O
for	O
many	O
reasons	O
,	O
e.g.	O
,	O
cases	O
when	O
the	O
database	O
is	O
found	O
corrupted	O
due	O
to	O
a	O
software	O
error	O
,	O
or	O
if	O
it	O
has	O
been	O
updated	O
with	O
erroneous	O
data	B-General_Concept
)	O
.	O
</s>
<s>
To	O
achieve	O
this	O
,	O
a	O
backup	O
operation	O
is	O
done	O
occasionally	O
or	O
continuously	O
,	O
where	O
each	O
desired	O
database	O
state	O
(	O
i.e.	O
,	O
the	O
values	O
of	O
its	O
data	B-General_Concept
and	O
their	O
embedding	O
in	O
database	O
's	O
data	B-General_Concept
structures	I-General_Concept
)	O
is	O
kept	O
within	O
dedicated	O
backup	O
files	O
(	O
many	O
techniques	O
exist	O
to	O
do	O
this	O
effectively	O
)	O
.	O
</s>
<s>
Static	O
analysis	O
techniques	O
for	O
software	O
verification	O
can	O
be	O
applied	O
also	O
in	O
the	O
scenario	O
of	O
query	B-Language
languages	I-Language
.	O
</s>
<s>
In	O
particular	O
,	O
the	O
*	O
Abstract	O
interpretation	O
framework	O
has	O
been	O
extended	O
to	O
the	O
field	O
of	O
query	B-Language
languages	I-Language
for	O
relational	B-Application
databases	I-Application
as	O
a	O
way	O
to	O
support	O
sound	O
approximation	O
techniques	O
.	O
</s>
<s>
The	O
semantics	O
of	O
query	B-Language
languages	I-Language
can	O
be	O
tuned	O
according	O
to	O
suitable	O
abstractions	O
of	O
the	O
concrete	O
domain	O
of	O
data	B-General_Concept
.	O
</s>
<s>
The	O
abstraction	O
of	O
relational	B-Application
database	I-Application
systems	O
has	O
many	O
interesting	O
applications	O
,	O
in	O
particular	O
,	O
for	O
security	O
purposes	O
,	O
such	O
as	O
fine-grained	O
access	O
control	O
,	O
watermarking	O
,	O
etc	O
.	O
</s>
<s>
Other	O
DBMS	B-General_Concept
features	O
might	O
include	O
:	O
</s>
<s>
Database	B-General_Concept
logs	I-General_Concept
–	O
This	O
helps	O
in	O
keeping	O
a	O
history	O
of	O
the	O
executed	O
functions	O
.	O
</s>
<s>
Graphics	O
component	O
for	O
producing	O
graphs	O
and	O
charts	O
,	O
especially	O
in	O
a	O
data	B-General_Concept
warehouse	O
system	O
.	O
</s>
<s>
Query	B-Language
optimizer	I-Language
–	O
Performs	O
query	B-Language
optimization	I-Language
on	O
every	O
query	B-Library
to	O
choose	O
an	O
efficient	O
query	B-Language
plan	I-Language
(	O
a	O
partial	O
order	O
(	O
tree	O
)	O
of	O
operations	O
)	O
to	O
be	O
executed	O
to	O
compute	O
the	O
query	B-Library
result	O
.	O
</s>
<s>
May	O
be	O
specific	O
to	O
a	O
particular	O
storage	B-General_Concept
engine	I-General_Concept
.	O
</s>
<s>
Tools	O
or	O
hooks	O
for	O
database	B-General_Concept
design	I-General_Concept
,	O
application	B-General_Concept
programming	I-General_Concept
,	O
application	O
program	O
maintenance	O
,	O
database	O
performance	O
analysis	O
and	O
monitoring	O
,	O
database	O
configuration	O
monitoring	O
,	O
DBMS	B-General_Concept
hardware	B-Architecture
configuration	O
(	O
a	O
DBMS	B-General_Concept
and	O
related	O
database	O
may	O
span	O
computers	O
,	O
networks	O
,	O
and	O
storage	O
units	O
)	O
and	O
related	O
database	O
mapping	O
(	O
especially	O
for	O
a	O
distributed	O
DBMS	B-General_Concept
)	O
,	O
storage	O
allocation	O
and	O
database	O
layout	O
monitoring	O
,	O
storage	O
migration	O
,	O
etc	O
.	O
</s>
<s>
Increasingly	O
,	O
there	O
are	O
calls	O
for	O
a	O
single	O
system	O
that	O
incorporates	O
all	O
of	O
these	O
core	O
functionalities	O
into	O
the	O
same	O
build	O
,	O
test	O
,	O
and	O
deployment	O
framework	O
for	O
database	B-Application
management	I-Application
and	O
source	O
control	O
.	O
</s>
<s>
The	O
first	O
task	O
of	O
a	O
database	O
designer	O
is	O
to	O
produce	O
a	O
conceptual	B-Application
data	I-Application
model	I-Application
that	O
reflects	O
the	O
structure	O
of	O
the	O
information	O
to	O
be	O
held	O
in	O
the	O
database	O
.	O
</s>
<s>
A	O
common	O
approach	O
to	O
this	O
is	O
to	O
develop	O
an	O
entity	B-Architecture
–	I-Architecture
relationship	I-Architecture
model	I-Architecture
,	O
often	O
with	O
the	O
aid	O
of	O
drawing	O
tools	O
.	O
</s>
<s>
Another	O
popular	O
approach	O
is	O
the	O
Unified	B-Language
Modeling	I-Language
Language	I-Language
.	O
</s>
<s>
A	O
successful	O
data	B-Application
model	I-Application
will	O
accurately	O
reflect	O
the	O
possible	O
state	O
of	O
the	O
external	O
world	O
being	O
modeled	O
:	O
for	O
example	O
,	O
if	O
people	O
can	O
have	O
more	O
than	O
one	O
phone	O
number	O
,	O
it	O
will	O
allow	O
this	O
information	O
to	O
be	O
captured	O
.	O
</s>
<s>
Designing	O
a	O
good	O
conceptual	B-Application
data	I-Application
model	I-Application
requires	O
a	O
good	O
understanding	O
of	O
the	O
application	O
domain	O
;	O
it	O
typically	O
involves	O
asking	O
deep	O
questions	O
about	O
the	O
things	O
of	O
interest	O
to	O
an	O
organization	O
,	O
like	O
"	O
can	O
a	O
customer	O
also	O
be	O
a	O
supplier	O
?	O
</s>
<s>
The	O
answers	O
to	O
these	O
questions	O
establish	O
definitions	O
of	O
the	O
terminology	O
used	O
for	O
entities	O
(	O
customers	O
,	O
products	O
,	O
flights	O
,	O
flight	O
segments	O
)	O
and	O
their	O
relationships	O
and	O
attributes	B-Language
.	O
</s>
<s>
Producing	O
the	O
conceptual	B-Application
data	I-Application
model	I-Application
sometimes	O
involves	O
input	O
from	O
business	O
processes	O
,	O
or	O
the	O
analysis	O
of	O
workflow	B-Operating_System
in	O
the	O
organization	O
.	O
</s>
<s>
For	O
example	O
,	O
it	O
can	O
help	O
when	O
deciding	O
whether	O
the	O
database	O
needs	O
to	O
hold	O
historic	O
data	B-General_Concept
as	O
well	O
as	O
current	O
data	B-General_Concept
.	O
</s>
<s>
Having	O
produced	O
a	O
conceptual	B-Application
data	I-Application
model	I-Application
that	O
users	O
are	O
happy	O
with	O
,	O
the	O
next	O
stage	O
is	O
to	O
translate	O
this	O
into	O
a	O
schema	B-Application
that	O
implements	O
the	O
relevant	O
data	B-General_Concept
structures	I-General_Concept
within	O
the	O
database	O
.	O
</s>
<s>
This	O
process	O
is	O
often	O
called	O
logical	O
database	B-General_Concept
design	I-General_Concept
,	O
and	O
the	O
output	O
is	O
a	O
logical	B-Application
data	I-Application
model	I-Application
expressed	O
in	O
the	O
form	O
of	O
a	O
schema	B-Application
.	O
</s>
<s>
Whereas	O
the	O
conceptual	B-Application
data	I-Application
model	I-Application
is	O
(	O
in	O
theory	B-General_Concept
at	O
least	O
)	O
independent	O
of	O
the	O
choice	O
of	O
database	O
technology	O
,	O
the	O
logical	B-Application
data	I-Application
model	I-Application
will	O
be	O
expressed	O
in	O
terms	O
of	O
a	O
particular	O
database	B-General_Concept
model	I-General_Concept
supported	O
by	O
the	O
chosen	O
DBMS	B-General_Concept
.	O
</s>
<s>
(	O
The	O
terms	O
data	B-Application
model	I-Application
and	O
database	B-General_Concept
model	I-General_Concept
are	O
often	O
used	O
interchangeably	O
,	O
but	O
in	O
this	O
article	O
we	O
use	O
data	B-Application
model	I-Application
for	O
the	O
design	O
of	O
a	O
specific	O
database	O
,	O
and	O
database	B-General_Concept
model	I-General_Concept
for	O
the	O
modeling	O
notation	O
used	O
to	O
express	O
that	O
design	O
)	O
.	O
</s>
<s>
The	O
most	O
popular	O
database	B-General_Concept
model	I-General_Concept
for	O
general-purpose	O
databases	B-Application
is	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
or	O
more	O
precisely	O
,	O
the	O
relational	B-Architecture
model	I-Architecture
as	O
represented	O
by	O
the	O
SQL	B-Language
language	I-Language
.	O
</s>
<s>
The	O
process	O
of	O
creating	O
a	O
logical	O
database	B-General_Concept
design	I-General_Concept
using	O
this	O
model	O
uses	O
a	O
methodical	O
approach	O
known	O
as	O
normalization	B-Application
.	O
</s>
<s>
The	O
goal	O
of	O
normalization	B-Application
is	O
to	O
ensure	O
that	O
each	O
elementary	O
"	O
fact	O
"	O
is	O
only	O
recorded	O
in	O
one	O
place	O
,	O
so	O
that	O
insertions	O
,	O
updates	O
,	O
and	O
deletions	O
automatically	O
maintain	O
consistency	B-General_Concept
.	O
</s>
<s>
The	O
final	O
stage	O
of	O
database	B-General_Concept
design	I-General_Concept
is	O
to	O
make	O
the	O
decisions	O
that	O
affect	O
performance	O
,	O
scalability	B-Architecture
,	O
recovery	O
,	O
security	O
,	O
and	O
the	O
like	O
,	O
which	O
depend	O
on	O
the	O
particular	O
DBMS	B-General_Concept
.	O
</s>
<s>
This	O
is	O
often	O
called	O
physical	O
database	B-General_Concept
design	I-General_Concept
,	O
and	O
the	O
output	O
is	O
the	O
physical	B-Application
data	I-Application
model	I-Application
.	O
</s>
<s>
A	O
key	O
goal	O
during	O
this	O
stage	O
is	O
data	B-General_Concept
independence	I-General_Concept
,	O
meaning	O
that	O
the	O
decisions	O
made	O
for	O
performance	O
optimization	O
purposes	O
should	O
be	O
invisible	O
to	O
end-users	O
and	O
applications	O
.	O
</s>
<s>
There	O
are	O
two	O
types	O
of	O
data	B-General_Concept
independence	I-General_Concept
:	O
Physical	B-General_Concept
data	I-General_Concept
independence	I-General_Concept
and	O
logical	B-General_Concept
data	I-General_Concept
independence	I-General_Concept
.	O
</s>
<s>
Physical	O
design	O
is	O
driven	O
mainly	O
by	O
performance	O
requirements	O
,	O
and	O
requires	O
a	O
good	O
knowledge	O
of	O
the	O
expected	O
workload	O
and	O
access	O
patterns	O
,	O
and	O
a	O
deep	O
understanding	O
of	O
the	O
features	O
offered	O
by	O
the	O
chosen	O
DBMS	B-General_Concept
.	O
</s>
<s>
Another	O
aspect	O
of	O
physical	O
database	B-General_Concept
design	I-General_Concept
is	O
security	O
.	O
</s>
<s>
It	O
involves	O
both	O
defining	O
access	O
control	O
to	O
database	O
objects	O
as	O
well	O
as	O
defining	O
security	O
levels	O
and	O
methods	O
for	O
the	O
data	B-General_Concept
itself	O
.	O
</s>
<s>
A	O
database	B-General_Concept
model	I-General_Concept
is	O
a	O
type	O
of	O
data	B-Application
model	I-Application
that	O
determines	O
the	O
logical	O
structure	O
of	O
a	O
database	O
and	O
fundamentally	O
determines	O
in	O
which	O
manner	O
data	B-General_Concept
can	O
be	O
stored	O
,	O
organized	O
,	O
and	O
manipulated	O
.	O
</s>
<s>
The	O
most	O
popular	O
example	O
of	O
a	O
database	B-General_Concept
model	I-General_Concept
is	O
the	O
relational	B-Architecture
model	I-Architecture
(	O
or	O
the	O
SQL	B-Language
approximation	O
of	O
relational	B-Architecture
)	O
,	O
which	O
uses	O
a	O
table-based	O
format	O
.	O
</s>
<s>
Common	O
logical	B-Application
data	I-Application
models	I-Application
for	O
databases	B-Application
include	O
:	O
</s>
<s>
An	O
object	B-General_Concept
–	I-General_Concept
relational	I-General_Concept
database	I-General_Concept
combines	O
the	O
two	O
related	O
structures	O
.	O
</s>
<s>
Physical	B-Application
data	I-Application
models	I-Application
include	O
:	O
</s>
<s>
Other	O
models	B-Application
include	O
:	O
</s>
<s>
Specialized	O
models	B-Application
are	O
optimized	O
for	O
particular	O
types	O
of	O
data	B-General_Concept
:	O
</s>
<s>
A	O
database	B-Application
management	I-Application
system	I-Application
provides	O
three	O
views	O
of	O
the	O
database	O
data	B-General_Concept
:	O
</s>
<s>
The	O
external	O
level	O
defines	O
how	O
each	O
group	O
of	O
end-users	O
sees	O
the	O
organization	O
of	O
data	B-General_Concept
in	O
the	O
database	O
.	O
</s>
<s>
It	O
is	O
out	O
of	O
the	O
scope	O
of	O
the	O
various	O
database	O
end-users	O
,	O
and	O
is	O
rather	O
of	O
interest	O
to	O
database	B-Application
application	I-Application
developers	B-Application
and	O
database	O
administrators	O
.	O
</s>
<s>
The	O
internal	O
level	O
(	O
or	O
physical	O
level	O
)	O
is	O
the	O
internal	O
organization	O
of	O
data	B-General_Concept
inside	O
a	O
DBMS	B-General_Concept
.	O
</s>
<s>
It	O
is	O
concerned	O
with	O
cost	O
,	O
performance	O
,	O
scalability	B-Architecture
and	O
other	O
operational	O
matters	O
.	O
</s>
<s>
It	O
deals	O
with	O
storage	O
layout	O
of	O
the	O
data	B-General_Concept
,	O
using	O
storage	O
structures	O
such	O
as	O
indexes	B-Data_Structure
to	O
enhance	O
performance	O
.	O
</s>
<s>
Occasionally	O
it	O
stores	O
data	B-General_Concept
of	O
individual	O
views	O
(	O
materialized	B-Application
views	I-Application
)	O
,	O
computed	O
from	O
generic	O
data	B-General_Concept
,	O
if	O
performance	O
justification	O
exists	O
for	O
such	O
redundancy	B-Application
.	O
</s>
<s>
While	O
there	O
is	O
typically	O
only	O
one	O
conceptual	O
and	O
internal	O
view	O
of	O
the	O
data	B-General_Concept
,	O
there	O
can	O
be	O
any	O
number	O
of	O
different	O
external	O
views	O
.	O
</s>
<s>
The	O
three-level	O
database	O
architecture	O
relates	O
to	O
the	O
concept	O
of	O
data	B-General_Concept
independence	I-General_Concept
which	O
was	O
one	O
of	O
the	O
major	O
initial	O
driving	O
forces	O
of	O
the	O
relational	B-Architecture
model	I-Architecture
.	O
</s>
<s>
On	O
the	O
one	O
hand	O
it	O
provides	O
a	O
common	O
view	O
of	O
the	O
database	O
,	O
independent	O
of	O
different	O
external	O
view	O
structures	O
,	O
and	O
on	O
the	O
other	O
hand	O
it	O
abstracts	O
away	O
details	O
of	O
how	O
the	O
data	B-General_Concept
are	O
stored	O
or	O
managed	O
(	O
internal	O
level	O
)	O
.	O
</s>
<s>
In	O
principle	O
every	O
level	O
,	O
and	O
even	O
every	O
external	O
view	O
,	O
can	O
be	O
presented	O
by	O
a	O
different	O
data	B-Application
model	I-Application
.	O
</s>
<s>
In	O
practice	O
usually	O
a	O
given	O
DBMS	B-General_Concept
uses	O
the	O
same	O
data	B-Application
model	I-Application
for	O
both	O
the	O
external	O
and	O
the	O
conceptual	O
levels	O
(	O
e.g.	O
,	O
relational	B-Architecture
model	I-Architecture
)	O
.	O
</s>
<s>
The	O
internal	O
level	O
,	O
which	O
is	O
hidden	O
inside	O
the	O
DBMS	B-General_Concept
and	O
depends	O
on	O
its	O
implementation	O
,	O
requires	O
a	O
different	O
level	O
of	O
detail	O
and	O
uses	O
its	O
own	O
types	O
of	O
data	B-General_Concept
structure	I-General_Concept
types	O
.	O
</s>
<s>
Research	O
activity	O
includes	O
theory	B-General_Concept
and	O
development	O
of	O
prototypes	B-Application
.	O
</s>
<s>
Notable	O
research	O
topics	O
have	O
included	O
models	B-Application
,	O
the	O
atomic	B-General_Concept
transaction	I-General_Concept
concept	O
,	O
related	O
concurrency	B-Operating_System
control	I-Operating_System
techniques	O
,	O
query	B-Language
languages	I-Language
and	O
query	B-Language
optimization	I-Language
methods	O
,	O
RAID	B-Architecture
,	O
and	O
more	O
.	O
</s>
<s>
The	O
database	O
research	O
area	O
has	O
several	O
dedicated	O
academic	O
journals	O
(	O
for	O
example	O
,	O
ACM	O
Transactions	B-General_Concept
on	O
Database	O
Systems-TODS	O
,	O
Data	B-General_Concept
and	O
Knowledge	O
Engineering-DKE	O
)	O
and	O
annual	O
conferences	O
(	O
e.g.	O
,	O
ACM	O
SIGMOD	O
,	O
ACM	O
PODS	O
,	O
VLDB	O
,	O
IEEE	O
ICDE	O
)	O
.	O
</s>
