<s>
A	O
data	B-Application
access	I-Application
layer	I-Application
(	O
DAL	O
)	O
in	O
computer	O
software	O
is	O
a	O
layer	B-Application
of	O
a	O
computer	B-Application
program	I-Application
which	O
provides	O
simplified	O
access	O
to	O
data	O
stored	O
in	O
persistent	B-Application
storage	I-Application
of	O
some	O
kind	O
,	O
such	O
as	O
an	O
entity-relational	B-Architecture
database	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
DAL	O
might	O
return	O
a	O
reference	O
to	O
an	O
object	O
(	O
in	O
terms	O
of	O
object-oriented	B-Language
programming	I-Language
)	O
complete	O
with	O
its	O
attributes	O
instead	O
of	O
a	O
row	B-Application
of	O
fields	B-Application
from	O
a	O
database	B-Application
table	I-Application
.	O
</s>
<s>
This	O
allows	O
the	O
client	B-Protocol
(	O
or	O
user	O
)	O
modules	O
to	O
be	O
created	O
with	O
a	O
higher	O
level	O
of	O
abstraction	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
instead	O
of	O
using	O
commands	O
such	O
as	O
insert	O
,	O
delete	O
,	O
and	O
update	O
to	O
access	O
a	O
specific	O
table	B-Application
in	O
a	O
database	O
,	O
a	O
class	O
and	O
a	O
few	O
stored	O
procedures	O
could	O
be	O
created	O
in	O
the	O
database	O
.	O
</s>
<s>
Or	O
,	O
the	O
insert	O
,	O
delete	O
and	O
update	O
commands	O
could	O
be	O
executed	O
within	O
simple	O
functions	O
like	O
registeruser	O
or	O
loginuser	O
stored	O
within	O
the	O
data	B-Application
access	I-Application
layer	I-Application
.	O
</s>
<s>
Also	O
,	O
business	O
logic	O
methods	O
from	O
an	O
application	O
can	O
be	O
mapped	O
to	O
the	O
data	B-Application
access	I-Application
layer	I-Application
.	O
</s>
<s>
Applications	O
using	O
a	O
data	B-Application
access	I-Application
layer	I-Application
can	O
be	O
either	O
database	O
server	O
dependent	O
or	O
independent	O
.	O
</s>
<s>
If	O
the	O
data	B-Application
access	I-Application
layer	I-Application
supports	O
multiple	O
database	O
types	O
,	O
the	O
application	O
becomes	O
able	O
to	O
use	O
whatever	O
databases	O
the	O
DAL	O
can	O
talk	O
to	O
.	O
</s>
<s>
In	O
either	O
circumstance	O
,	O
having	O
a	O
data	B-Application
access	I-Application
layer	I-Application
provides	O
a	O
centralized	O
location	O
for	O
all	O
calls	O
into	O
the	O
database	O
,	O
and	O
thus	O
makes	O
it	O
easier	O
to	O
port	O
the	O
application	O
to	O
other	O
database	O
systems	O
(	O
assuming	O
that	O
100%	O
of	O
the	O
database	O
interaction	O
is	O
done	O
in	O
the	O
DAL	O
for	O
a	O
given	O
application	O
)	O
.	O
</s>
<s>
Object-Relational	B-General_Concept
Mapping	I-General_Concept
tools	O
provide	O
data	O
layers	O
in	O
this	O
fashion	O
,	O
following	O
the	O
Active	O
Record	O
or	O
Data	O
Mapper	O
patterns	O
.	O
</s>
<s>
The	O
ORM/active	O
-record	O
model	O
is	O
popular	O
with	O
web	O
frameworks	O
.	O
</s>
