<s>
In	O
computing	O
,	O
the	O
term	O
virtual	B-General_Concept
directory	I-General_Concept
has	O
a	O
couple	O
of	O
meanings	O
.	O
</s>
<s>
It	O
may	O
simply	O
designate	O
(	O
for	O
example	O
in	O
IIS	B-Application
)	O
a	O
folder	O
which	O
appears	O
in	O
a	O
path	B-Application
but	O
which	O
is	O
not	O
actually	O
a	O
subfolder	O
of	O
the	O
preceding	O
folder	O
in	O
the	O
path	B-Application
.	O
</s>
<s>
A	O
virtual	B-General_Concept
directory	I-General_Concept
or	O
virtual	B-General_Concept
directory	I-General_Concept
server	O
(	O
VDS	O
)	O
in	O
this	O
context	O
is	O
a	O
software	O
layer	O
that	O
delivers	O
a	O
single	O
access	O
point	O
for	O
identity	O
management	O
applications	O
and	O
service	O
platforms	O
.	O
</s>
<s>
A	O
virtual	B-General_Concept
directory	I-General_Concept
operates	O
as	O
a	O
high-performance	O
,	O
lightweight	O
abstraction	O
layer	O
that	O
resides	O
between	O
client	O
applications	O
and	O
disparate	O
types	O
of	O
identity-data	O
repositories	O
,	O
such	O
as	O
proprietary	O
and	O
standard	O
directories	O
,	O
databases	O
,	O
web	O
services	O
,	O
and	O
applications	O
.	O
</s>
<s>
A	O
virtual	B-General_Concept
directory	I-General_Concept
receives	O
queries	O
and	O
directs	O
them	O
to	O
the	O
appropriate	O
data	O
sources	O
by	O
abstracting	O
and	O
virtualizing	O
data	O
.	O
</s>
<s>
The	O
virtual	B-General_Concept
directory	I-General_Concept
integrates	O
identity	O
data	O
from	O
multiple	O
heterogeneous	O
data	O
stores	O
and	O
presents	O
it	O
as	O
though	O
it	O
were	O
coming	O
from	O
one	O
source	O
.	O
</s>
<s>
This	O
ability	O
to	O
reach	O
into	O
disparate	O
repositories	O
makes	O
virtual	B-General_Concept
directory	I-General_Concept
technology	O
ideal	O
for	O
consolidating	O
data	O
stored	O
in	O
a	O
distributed	O
environment	O
.	O
</s>
<s>
,	O
virtual	B-General_Concept
directory	I-General_Concept
servers	O
most	O
commonly	O
use	O
the	O
LDAP	B-Protocol
protocol	O
,	O
but	O
more	O
sophisticated	O
virtual	B-General_Concept
directories	I-General_Concept
can	O
also	O
support	O
SQL	B-Language
as	O
well	O
as	O
DSML	B-General_Concept
and	O
SPML	O
.	O
</s>
<s>
Industry	O
experts	O
have	O
heralded	O
the	O
importance	O
of	O
the	O
virtual	B-General_Concept
directory	I-General_Concept
in	O
modernizing	O
the	O
identity	O
infrastructure	O
.	O
</s>
<s>
According	O
to	O
Dave	O
Kearns	O
of	O
Network	O
World	O
,	O
"	O
Virtualization	O
is	O
hot	O
and	O
a	O
virtual	B-General_Concept
directory	I-General_Concept
is	O
the	O
building	O
block	O
,	O
or	O
foundation	O
,	O
you	O
should	O
be	O
looking	O
at	O
for	O
your	O
next	O
identity	O
management	O
project.	O
"	O
</s>
<s>
In	O
addition	O
,	O
Gartner	O
analyst	O
,	O
Bob	O
Blakley	O
said	O
that	O
virtual	B-General_Concept
directories	I-General_Concept
are	O
playing	O
an	O
increasingly	O
vital	O
role	O
.	O
</s>
<s>
Virtual	B-General_Concept
directories	I-General_Concept
can	O
have	O
some	O
or	O
all	O
of	O
the	O
following	O
capabilities	O
:	O
</s>
<s>
Virtual	B-General_Concept
directories	I-General_Concept
:	O
</s>
<s>
An	O
original	O
disadvantage	O
is	O
public	O
perception	O
of	O
"	O
push	O
&	O
pull	O
technologies	O
"	O
which	O
is	O
the	O
general	O
classification	O
of	O
"	O
virtual	B-General_Concept
directories	I-General_Concept
"	O
depending	O
on	O
the	O
nature	O
of	O
their	O
deployment	O
.	O
</s>
<s>
Virtual	B-General_Concept
directories	I-General_Concept
were	O
initially	O
designed	O
and	O
later	O
deployed	O
with	O
"	O
push	O
technologies	O
"	O
in	O
mind	O
,	O
which	O
also	O
contravened	O
with	O
privacy	O
laws	O
of	O
the	O
United	O
States	O
.	O
</s>
<s>
The	O
classical	O
virtual	B-General_Concept
directory	I-General_Concept
based	O
on	O
proxy	O
cannot	O
modify	O
underlying	O
data	O
structures	O
or	O
create	O
new	O
views	O
based	O
on	O
the	O
relationships	O
of	O
data	O
from	O
across	O
multiple	O
systems	O
.	O
</s>
<s>
So	O
if	O
an	O
application	O
requires	O
a	O
different	O
structure	O
,	O
such	O
as	O
a	O
flattened	O
list	O
of	O
identities	O
,	O
or	O
a	O
deeper	O
hierarchy	O
for	O
delegated	O
administration	O
,	O
a	O
virtual	B-General_Concept
directory	I-General_Concept
is	O
limited	O
.	O
</s>
<s>
Virtual	B-General_Concept
directories	I-General_Concept
without	O
advanced	O
caching	O
technologies	O
cannot	O
scale	O
to	O
heterogeneous	O
,	O
high-volume	O
environments	O
.	O
</s>
<s>
For	O
instance	O
,	O
if	O
one	O
directory	O
has	O
the	O
namespace	O
"	O
ou	O
=	O
internal	O
,	O
dc	O
=	O
domain	O
,	O
dc	O
=	O
com	O
"	O
and	O
a	O
second	O
directory	O
has	O
the	O
namespace	O
"	O
ou	O
=	O
external	O
,	O
dc	O
=	O
domain	O
,	O
dc	O
=	O
com	O
,	O
"	O
then	O
creating	O
a	O
virtual	B-General_Concept
directory	I-General_Concept
with	O
both	O
namespaces	O
is	O
an	O
example	O
of	O
namespace	O
joining	O
.	O
</s>
<s>
Data	O
remapping	O
:	O
The	O
translation	O
of	O
data	O
inside	O
of	O
the	O
virtual	B-General_Concept
directory	I-General_Concept
.	O
</s>
<s>
For	O
instance	O
,	O
mapping	O
“	O
uid	O
”	O
to	O
“	O
samaccountname	O
,	O
”	O
so	O
a	O
client	O
application	O
that	O
only	O
supports	O
a	O
standard	O
LDAP-compliant	O
data	O
source	O
is	O
able	O
to	O
search	O
an	O
Active	O
Directory	O
namespace	O
,	O
as	O
well	O
.	O
</s>
<s>
Identity	O
routing	O
:	O
Virtual	B-General_Concept
directories	I-General_Concept
may	O
support	O
the	O
routing	O
of	O
requests	O
based	O
on	O
certain	O
criteria	O
(	O
such	O
as	O
write	O
operations	O
going	O
to	O
a	O
master	O
while	O
read	O
operations	O
being	O
forwarded	O
to	O
replicas	O
)	O
.	O
</s>
<s>
Authoritative	O
source	O
:	O
A	O
"	O
virtualized	O
"	O
data	O
repository	O
,	O
such	O
as	O
a	O
directory	O
or	O
database	O
,	O
that	O
the	O
virtual	B-General_Concept
directory	I-General_Concept
can	O
trust	O
for	O
user	O
data	O
.	O
</s>
<s>
The	O
following	O
are	O
sample	O
use	O
cases	O
of	O
virtual	B-General_Concept
directories	I-General_Concept
:	O
</s>
<s>
Centralizing	O
identity	O
storage	O
across	O
the	O
infrastructure	O
,	O
making	O
identity	O
information	O
available	O
to	O
applications	O
through	O
various	O
protocols	O
(	O
including	O
LDAP	B-Protocol
,	O
JDBC	O
,	O
and	O
web	O
services	O
)	O
.	O
</s>
