<s>
Shadow	B-Application
tables	I-Application
are	O
objects	O
in	O
computer	B-General_Concept
science	I-General_Concept
used	O
to	O
improve	O
the	O
way	O
machines	O
,	O
networks	O
and	O
programs	O
handle	O
information	O
.	O
</s>
<s>
More	O
specifically	O
,	O
a	O
shadow	B-Application
table	I-Application
is	O
an	O
object	O
that	O
is	O
read	O
and	O
written	O
by	O
a	O
processor	O
and	O
contains	O
data	O
similar	O
to	O
(	O
in	O
the	O
same	O
format	O
as	O
)	O
its	O
primary	O
table	O
,	O
which	O
is	O
the	O
table	O
it	O
's	O
"	O
shadowing	O
"	O
.	O
</s>
<s>
Shadow	B-Application
tables	I-Application
usually	O
contain	O
data	O
that	O
is	O
relevant	O
to	O
the	O
operation	O
and	O
maintenance	O
of	O
its	O
primary	O
table	O
,	O
but	O
not	O
within	O
the	O
subset	O
of	O
data	O
required	O
for	O
the	O
primary	O
table	O
to	O
exist	O
.	O
</s>
<s>
Shadow	B-Application
tables	I-Application
are	O
related	O
to	O
the	O
data	O
type	O
"	O
trails	O
"	O
in	O
data	O
storage	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Trails	O
are	O
very	O
similar	O
to	O
shadow	B-Application
tables	I-Application
but	O
instead	O
of	O
storing	O
identically	O
formatted	O
information	O
that	O
is	O
different	O
(	O
like	O
shadow	B-Application
tables	I-Application
)	O
,	O
they	O
store	O
a	O
history	O
of	O
modifications	O
and	O
functions	O
operated	O
on	O
a	O
table	O
.	O
</s>
<s>
Shadow	B-Application
tables	I-Application
,	O
as	O
an	O
abstract	O
concept	O
,	O
have	O
been	O
used	O
since	O
the	O
beginning	O
of	O
modern	O
computing	O
.	O
</s>
<s>
However	O
,	O
widespread	O
usage	O
of	O
the	O
specific	O
phrase	O
"	O
shadow	B-Application
table	I-Application
"	O
began	O
when	O
relational	B-Application
database	I-Application
management	I-Application
systems	I-Application
(	O
RDBMS	O
)	O
became	O
widely	O
used	O
in	O
the	O
1970s	O
.	O
</s>
<s>
The	O
initial	O
usage	O
of	O
relational	O
DBMs	O
for	O
commercial	O
purposes	O
lead	O
to	O
the	O
term	O
"	O
shadow	B-Application
tables	I-Application
"	O
becoming	O
widespread	O
.	O
</s>
<s>
Since	O
shadow	B-Application
tables	I-Application
are	O
such	O
an	O
abstract	O
concept	O
,	O
their	O
applications	O
remain	O
in	O
the	O
realm	O
of	O
computer	B-General_Concept
science	I-General_Concept
.	O
</s>
<s>
Shadow	B-Application
tables	I-Application
are	O
usually	O
used	O
in	O
order	O
to	O
improve	O
the	O
performance	O
,	O
capacity	O
,	O
and	O
ability	O
of	O
an	O
existing	O
computer/network	O
system	O
.	O
</s>
<s>
In	O
most	O
applications	O
,	O
shadow	B-Application
tables	I-Application
are	O
usually	O
a	O
carbon	O
copy	O
of	O
their	O
primary	O
tables	O
 '	O
structure	O
,	O
but	O
with	O
unique	O
data	O
.	O
</s>
<s>
Since	O
shadow	B-Application
tables	I-Application
are	O
a	O
specific	O
type	O
of	O
object	O
in	O
computer	B-General_Concept
science	I-General_Concept
,	O
the	O
applications	O
vary	O
greatly	O
,	O
because	O
their	O
application	O
depends	O
on	O
what	O
data	O
is	O
stored	O
in	O
the	O
shadow	B-Application
table	I-Application
and	O
how	O
that	O
data	O
is	O
used	O
.	O
</s>
<s>
The	O
following	O
is	O
a	O
list	O
of	O
general	O
,	O
abstract	O
applications	O
for	O
shadow	B-Application
tables	I-Application
that	O
span	O
all	O
real-world	O
applications	O
.	O
</s>
<s>
Storage	B-General_Concept
-	O
The	O
storage	B-General_Concept
of	O
a	O
data	O
entry	O
in	O
a	O
shadow	B-Application
table	I-Application
that	O
would	O
have	O
normally	O
been	O
deleted	O
or	O
modified	O
.	O
</s>
<s>
Encapsulation	B-Application
-	O
The	O
placement	O
of	O
data	O
within	O
a	O
shadow	B-Application
table	I-Application
in	O
order	O
to	O
separate	O
a	O
set	O
of	O
data	O
from	O
another	O
.	O
</s>
<s>
Modularity	B-Architecture
-	O
The	O
placement	O
of	O
data	O
within	O
a	O
shadow	B-Application
table	I-Application
to	O
make	O
modification	O
and	O
handling	O
of	O
the	O
data	O
easier	O
.	O
</s>
<s>
When	O
shadow	B-Application
tables	I-Application
are	O
used	O
to	O
solve	O
current	O
problems	O
in	O
today	O
's	O
computer/network	O
systems	O
,	O
usually	O
a	O
combination	O
of	O
more	O
than	O
one	O
of	O
the	O
aforementioned	O
theoretical/abstract	O
applications	O
of	O
shadow	B-Application
tables	I-Application
are	O
used	O
.	O
</s>
<s>
The	O
following	O
list	O
is	O
a	O
very	O
tiny	O
subset	O
of	O
all	O
real-world	O
applications	O
of	O
shadow	B-Application
tables	I-Application
and	O
is	O
only	O
shown	O
to	O
give	O
an	O
example	O
of	O
common	O
applications	O
of	O
shadow	B-Application
tables	I-Application
.	O
</s>
<s>
Database	B-Application
management	I-Application
systems	I-Application
(	O
DBMS	O
)	O
are	O
software	O
that	O
handle	O
the	O
maintenance	O
,	O
security	O
,	O
and	O
manipulation	O
of	O
data	O
tables	O
.	O
</s>
<s>
Well	O
known	O
and	O
widely	O
used	O
examples	O
of	O
DBMS	O
 '	O
are	O
SQL	B-Language
Server	O
,	O
MySQL	O
,	O
Oracle	O
and	O
PostgreSQL	O
.	O
</s>
<s>
Each	O
of	O
these	O
DBMS	O
 '	O
create	O
a	O
virtual	O
"	O
environment	O
"	O
in	O
which	O
tables	O
of	O
data	O
are	O
held	O
and	O
can	O
be	O
read	O
and	O
written	O
to	O
via	O
a	O
specific	O
type	O
of	O
programming	O
language	O
known	O
as	O
a	O
query	B-Language
language	I-Language
.	O
</s>
<s>
Query	B-Language
languages	I-Language
specialize	O
in	O
the	O
simple	O
modification	O
or	O
retrieval	O
of	O
large	O
and	O
specific	O
amounts	O
of	O
data	O
.	O
</s>
<s>
Most	O
modern	O
DBMS	O
 '	O
specifically	O
support	O
SQL(a specific type of query language )	O
.	O
</s>
<s>
Using	O
SQL	B-Language
,	O
one	O
can	O
easily	O
create	O
tables	O
that	O
share	O
the	O
same	O
structure	O
as	O
already	O
existing	O
tables	O
.	O
</s>
<s>
SQL	B-Language
can	O
also	O
get	O
data	O
written	O
to	O
these	O
new	O
tables	O
,	O
creating	O
a	O
shadow	B-Application
table	I-Application
.	O
</s>
<s>
Shadow	B-Application
tables	I-Application
are	O
often	O
used	O
with	O
DBMS	O
 '	O
to	O
improve	O
efficiency	O
by	O
preventing	O
redundant	O
operations	O
being	O
performed	O
by	O
the	O
DBM	O
.	O
</s>
<s>
Shadow	B-Application
tables	I-Application
are	O
also	O
easy	O
to	O
implement	O
in	O
most	O
modern	O
DBMS	O
 '	O
because	O
they	O
do	O
not	O
affect	O
the	O
original	O
data	O
,	O
so	O
the	O
way	O
the	O
databases	B-Application
and	O
applications	O
accessing	O
them	O
work	O
together	O
is	O
not	O
affected	O
,	O
unless	O
desired	O
.	O
</s>
<s>
For	O
example	O
,	O
shadow	B-Application
tables	I-Application
could	O
be	O
used	O
in	O
an	O
efficient	O
backup	O
system	O
that	O
supports	O
large	O
data	O
tables	O
that	O
rarely	O
change	O
.	O
</s>
<s>
Without	O
shadow	B-Application
tables	I-Application
,	O
one	O
could	O
create	O
a	O
program	O
that	O
simply	O
saves	O
a	O
version	O
of	O
that	O
table	O
every	O
day	O
.	O
</s>
<s>
With	O
shadow	B-Application
tables	I-Application
,	O
one	O
could	O
create	O
an	O
empty	O
"	O
shadow	B-Application
table	I-Application
"	O
of	O
that	O
table	O
and	O
use	O
a	O
program	O
that	O
inserts	O
a	O
copy	O
of	O
a	O
row	O
into	O
the	O
shadow	B-Application
table	I-Application
every	O
time	O
that	O
row	O
gets	O
deleted	O
from	O
the	O
primary	O
table	O
.	O
</s>
<s>
After	O
50	O
days	O
using	O
the	O
shadow	B-Application
table	I-Application
system	O
in	O
the	O
worst-case	O
scenario	O
,	O
there	O
would	O
be	O
one	O
copy	O
of	O
the	O
primary	O
table	O
,	O
assuming	O
every	O
row	O
in	O
the	O
primary	O
table	O
got	O
deleted	O
.	O
</s>
<s>
Interfacing	B-Application
is	O
the	O
process	O
of	O
using	O
"	O
layers	O
"	O
to	O
simplify	O
the	O
communications	O
between	O
technologies	O
and	O
between	O
people	O
and	O
technologies	O
.	O
</s>
<s>
One	O
example	O
of	O
layered	O
interfacing	B-Application
is	O
the	O
buttons	O
and	O
menus	O
used	O
by	O
home	O
computer	O
operating	O
systems	O
.	O
</s>
<s>
Shadow	B-Application
tables	I-Application
are	O
often	O
used	O
as	O
layers	O
between	O
the	O
end-user	O
and	O
the	O
database	O
.	O
</s>
<s>
The	O
database	O
can	O
send	O
a	O
shadow	B-Application
table	I-Application
that	O
only	O
contains	O
the	O
transactions	O
involving	O
the	O
user	O
that	O
requested	O
his/her	O
transaction	O
history	O
.	O
</s>
<s>
Shadow	O
page	B-General_Concept
tables	I-General_Concept
are	O
often	O
used	O
in	O
simulating	O
more	O
than	O
one	O
operating	O
system	O
on	O
a	O
single	O
set	O
of	O
memory	O
and	O
processor	O
.	O
</s>
<s>
A	O
page	B-General_Concept
table	I-General_Concept
is	O
used	O
by	O
an	O
operating	O
system	O
to	O
map	O
the	O
virtual	B-Architecture
memory	I-Architecture
,	O
the	O
actual	O
memory	O
used	O
by	O
programs	O
and	O
the	O
operating	O
system	O
to	O
store	O
information	O
,	O
to	O
its	O
location	O
on	O
the	O
physical	O
memory	O
,	O
the	O
hardware-specific	O
memory	O
stored	O
in	O
bytes	O
on	O
the	O
RAM	O
(	O
Random	O
Access	O
Memory	O
)	O
.	O
</s>
<s>
A	O
shadow	O
page	B-General_Concept
table	I-General_Concept
is	O
a	O
pseudo-page	O
table	O
within	O
a	O
computer	O
's	O
main	O
page	B-General_Concept
table	I-General_Concept
which	O
allows	O
a	O
system	O
to	O
run	O
more	O
than	O
one	O
kind	O
of	O
operating	O
system	O
concurrently	O
.	O
</s>
