<s>
Federated	B-Operating_System
search	I-Operating_System
retrieves	O
information	O
from	O
a	O
variety	O
of	O
sources	O
via	O
a	O
search	O
application	O
built	O
on	O
top	O
of	O
one	O
or	O
more	O
search	B-Application
engines	I-Application
.	O
</s>
<s>
A	O
user	O
makes	O
a	O
single	O
query	O
request	O
which	O
is	O
distributed	O
to	O
the	O
search	B-Application
engines	I-Application
,	O
databases	O
or	O
other	O
query	O
engines	O
participating	O
in	O
the	O
federation	O
.	O
</s>
<s>
The	O
federated	B-Operating_System
search	I-Operating_System
then	O
aggregates	O
the	O
results	O
that	O
are	O
received	O
from	O
the	O
search	B-Application
engines	I-Application
for	O
presentation	O
to	O
the	O
user	O
.	O
</s>
<s>
Federated	B-Operating_System
search	I-Operating_System
can	O
be	O
used	O
to	O
integrate	O
disparate	O
information	O
resources	O
within	O
a	O
single	O
large	O
organization	O
(	O
"	O
enterprise	O
"	O
)	O
or	O
for	O
the	O
entire	O
web	O
.	O
</s>
<s>
Federated	B-Operating_System
search	I-Operating_System
,	O
unlike	O
distributed	O
search	O
,	O
requires	O
centralized	O
coordination	O
of	O
the	O
searchable	B-Application
resources	O
.	O
</s>
<s>
This	O
involves	O
both	O
coordination	O
of	O
the	O
queries	O
transmitted	O
to	O
the	O
individual	O
search	B-Application
engines	I-Application
and	O
fusion	O
of	O
the	O
search	B-Application
results	I-Application
returned	O
by	O
each	O
of	O
them	O
.	O
</s>
<s>
Federated	B-Operating_System
search	I-Operating_System
came	O
about	O
to	O
meet	O
the	O
need	O
of	O
searching	O
multiple	O
disparate	O
content	O
sources	O
with	O
one	O
query	O
.	O
</s>
<s>
Other	O
approaches	O
include	O
constructing	O
an	O
Enterprise	O
data	O
warehouse	O
,	O
Data	B-General_Concept
lake	I-General_Concept
,	O
or	O
Data	B-Application
hub	I-Application
.	O
</s>
<s>
Federated	B-Operating_System
Search	I-Operating_System
queries	O
many	O
times	O
in	O
many	O
ways	O
(	O
each	O
source	O
is	O
queried	O
separately	O
)	O
where	O
other	O
approaches	O
import	O
and	O
transform	O
data	O
many	O
times	O
,	O
typically	O
in	O
overnight	O
batch	O
processes	O
.	O
</s>
<s>
Federated	B-Operating_System
search	I-Operating_System
provides	O
a	O
real-time	O
view	O
of	O
all	O
sources	O
(	O
to	O
the	O
extent	O
they	O
are	O
all	O
online	O
and	O
available	O
)	O
.	O
</s>
<s>
In	O
industrial	O
search	B-Application
engines	I-Application
,	O
such	O
as	O
LinkedIn	B-Application
,	O
federated	B-Operating_System
search	I-Operating_System
is	O
used	O
to	O
personalize	O
vertical	O
preference	O
for	O
ambiguous	O
queries	O
.	O
</s>
<s>
For	O
instance	O
,	O
when	O
a	O
user	O
issues	O
a	O
query	O
like	O
"	O
machine	O
learning	O
"	O
on	O
LinkedIn	B-Application
,	O
he	O
or	O
she	O
could	O
mean	O
to	O
search	O
for	O
people	O
with	O
machine	O
learning	O
skill	O
,	O
jobs	O
requiring	O
machine	O
learning	O
skill	O
or	O
content	O
about	O
the	O
topic	O
.	O
</s>
<s>
In	O
such	O
cases	O
,	O
federated	B-Operating_System
search	I-Operating_System
could	O
exploit	O
user	O
intent	O
(	O
e.g.	O
,	O
hiring	O
,	O
job	O
seeking	O
or	O
content	O
consuming	O
)	O
to	O
personalize	O
the	O
vertical	O
order	O
for	O
each	O
individual	O
user	O
.	O
</s>
<s>
As	O
described	O
by	O
Peter	O
Jacso	O
(	O
2004	O
)	O
,	O
federated	B-Operating_System
searching	I-Operating_System
consists	O
of	O
(	O
1	O
)	O
transforming	O
a	O
query	O
and	O
broadcasting	O
it	O
to	O
a	O
group	O
of	O
disparate	O
databases	O
or	O
other	O
web	O
resources	O
,	O
with	O
the	O
appropriate	O
syntax	O
,	O
(	O
2	O
)	O
merging	O
the	O
results	O
collected	O
from	O
the	O
databases	O
,	O
(	O
3	O
)	O
presenting	O
them	O
in	O
a	O
succinct	O
and	O
unified	O
format	O
with	O
minimal	O
duplication	O
,	O
and	O
(	O
4	O
)	O
providing	O
a	O
means	O
,	O
performed	O
either	O
automatically	O
or	O
by	O
the	O
portal	O
user	O
,	O
to	O
sort	O
the	O
merged	O
result	O
set	O
.	O
</s>
<s>
Federated	B-Operating_System
search	I-Operating_System
portals	O
,	O
either	O
commercial	O
or	O
open	O
access	O
,	O
generally	O
search	O
public	O
access	O
bibliographic	B-Library
databases	I-Library
,	O
public	O
access	O
Web-based	O
library	O
catalogues	O
(	O
OPACs	O
)	O
,	O
Web-based	O
search	B-Application
engines	I-Application
like	O
Google	B-Application
and/or	O
open-access	O
,	O
government-operated	O
or	O
corporate	O
data	O
collections	O
.	O
</s>
<s>
This	O
process	O
allows	O
federated	B-Operating_System
search	I-Operating_System
some	O
key	O
advantages	O
when	O
compared	O
with	O
existing	O
crawler-based	O
search	B-Application
engines	I-Application
.	O
</s>
<s>
Federated	B-Operating_System
search	I-Operating_System
need	O
not	O
place	O
any	O
requirements	O
or	O
burdens	O
on	O
owners	O
of	O
the	O
individual	O
information	O
sources	O
,	O
other	O
than	O
handling	O
increased	O
traffic	O
.	O
</s>
<s>
Federated	B-Operating_System
searches	I-Operating_System
are	O
inherently	O
as	O
current	O
as	O
the	O
individual	O
information	O
sources	O
,	O
as	O
they	O
are	O
searched	O
in	O
real	O
time	O
.	O
</s>
<s>
One	O
application	O
of	O
federated	B-Operating_System
searching	I-Operating_System
is	O
the	O
metasearch	B-Application
engine	I-Application
.	O
</s>
<s>
However	O
,	O
the	O
metasearch	B-Application
approach	O
does	O
not	O
overcome	O
the	O
shortcomings	O
of	O
the	O
component	O
search	B-Application
engines	I-Application
,	O
such	O
as	O
incomplete	O
indexes	O
.	O
</s>
<s>
Documents	O
that	O
are	O
not	O
indexed	O
by	O
search	B-Application
engines	I-Application
create	O
what	O
is	O
known	O
as	O
the	O
deep	O
Web	O
,	O
or	O
invisible	O
Web	O
.	O
</s>
<s>
Google	B-Library
Scholar	I-Library
is	O
one	O
example	O
of	O
many	O
projects	O
trying	O
to	O
address	O
this	O
,	O
by	O
indexing	O
electronic	O
documents	O
that	O
search	B-Application
engines	I-Application
ignore	O
.	O
</s>
<s>
And	O
the	O
metasearch	B-Application
approach	O
,	O
like	O
the	O
underlying	O
search	B-Application
engine	I-Application
technology	O
,	O
only	O
works	O
with	O
information	O
sources	O
stored	O
in	O
electronic	O
form	O
.	O
</s>
<s>
One	O
of	O
the	O
main	O
challenges	O
of	O
metasearch	B-Application
,	O
is	O
ensuring	O
that	O
the	O
search	O
query	O
is	O
compatible	O
with	O
the	O
component	O
search	B-Application
engines	I-Application
that	O
are	O
being	O
federated	O
and	O
combined	O
.	O
</s>
<s>
When	O
the	O
search	O
vocabulary	O
or	O
data	B-Application
model	I-Application
of	O
the	O
search	O
system	O
is	O
different	O
from	O
the	O
data	B-Application
model	I-Application
of	O
one	O
or	O
more	O
of	O
the	O
foreign	O
target	O
systems	O
,	O
the	O
query	O
must	O
be	O
translated	O
into	O
each	O
of	O
the	O
foreign	O
target	O
systems	O
.	O
</s>
<s>
This	O
can	O
be	O
done	O
using	O
simple	O
data-element	O
translation	O
or	O
may	O
require	O
semantic	B-Application
translation	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
if	O
one	O
search	B-Application
engine	I-Application
allows	O
for	O
quoting	O
of	O
exact	O
strings	O
or	O
n-grams	B-Language
and	O
another	O
does	O
not	O
,	O
the	O
query	O
must	O
be	O
translated	O
to	O
be	O
compatible	O
with	O
each	O
search	B-Application
engine	I-Application
.	O
</s>
<s>
To	O
translate	O
a	O
quoted	O
exact	O
string	O
query	O
,	O
it	O
can	O
be	O
broken	O
down	O
into	O
a	O
set	O
of	O
overlapping	O
N-grams	B-Language
that	O
are	O
most	O
likely	O
to	O
give	O
the	O
desired	O
search	B-Application
results	I-Application
in	O
each	O
search	B-Application
engine	I-Application
.	O
</s>
<s>
Another	O
challenge	O
faced	O
in	O
the	O
implementation	O
of	O
federated	B-Operating_System
search	I-Operating_System
engines	O
is	O
scalability	O
.	O
</s>
<s>
It	O
is	O
difficult	O
to	O
maintain	O
the	O
performance	O
,	O
the	O
response	O
speed	O
,	O
of	O
a	O
federated	B-Operating_System
search	I-Operating_System
engine	O
as	O
it	O
combines	O
more	O
and	O
more	O
information	O
sources	O
together	O
.	O
</s>
<s>
One	O
implementation	O
of	O
federated	B-Operating_System
search	I-Operating_System
that	O
has	O
begun	O
to	O
address	O
this	O
issue	O
is	O
WorldWideScience	B-Application
,	O
hosted	O
by	O
the	O
U.S.	O
Department	O
of	O
Energy	O
's	O
Office	O
of	O
Scientific	O
and	O
Technical	O
Information	O
.	O
</s>
<s>
WorldWideScience	B-Application
is	O
composed	O
of	O
more	O
than	O
40	O
information	O
sources	O
,	O
several	O
of	O
which	O
are	O
federated	B-Operating_System
search	I-Operating_System
portals	O
themselves	O
.	O
</s>
<s>
Science.gov	O
returns	O
its	O
highest	O
ranked	O
results	O
to	O
WorldWideScience	B-Application
,	O
which	O
then	O
merges	O
and	O
ranks	O
these	O
results	O
with	O
the	O
search	O
returned	O
by	O
the	O
other	O
information	O
sources	O
that	O
comprise	O
WorldWideScience	B-Application
.	O
</s>
<s>
This	O
approach	O
of	O
cascaded	O
federated	B-Operating_System
search	I-Operating_System
enables	O
large	O
number	O
of	O
information	O
sources	O
to	O
be	O
searched	O
via	O
a	O
single	O
query	O
.	O
</s>
<s>
Another	O
application	O
Sesam	O
running	O
in	O
both	O
Norway	O
and	O
Sweden	O
has	O
been	O
built	O
on	O
top	O
of	O
an	O
open	O
sourced	O
platform	O
specialised	O
for	O
federated	B-Operating_System
search	I-Operating_System
solutions	O
.	O
</s>
<s>
To	O
personalize	O
vertical	O
orders	O
in	O
federated	B-Operating_System
search	I-Operating_System
,	O
LinkedIn	B-Application
search	B-Application
engine	I-Application
exploits	O
the	O
searcher	O
's	O
profile	O
and	O
recent	O
activities	O
to	O
infer	O
his	O
or	O
her	O
intent	O
,	O
such	O
as	O
hiring	O
,	O
job	O
seeking	O
and	O
content	O
consuming	O
,	O
then	O
uses	O
the	O
intent	O
,	O
along	O
with	O
many	O
other	O
signals	O
,	O
to	O
rank	O
vertical	O
order	O
that	O
personally	O
relevant	O
to	O
the	O
individual	O
searcher	O
.	O
</s>
<s>
SWIRL	O
Search	O
is	O
an	O
open	O
source	O
federated	B-Operating_System
search	I-Operating_System
engine	O
,	O
released	O
under	O
the	O
Apache	O
2.0	O
license	O
.	O
</s>
<s>
It	O
includes	O
pre-built	O
connectors	O
to	O
popular	O
open	O
source	O
search	B-Application
engines	I-Application
,	O
and	O
re-ranks	O
results	O
using	O
cosine	O
vector	O
similarity	O
.	O
</s>
<s>
to	O
each	O
underlying	O
search	B-Application
engine	I-Application
,	O
so	O
that	O
appropriate	O
security	O
is	O
maintained	O
.	O
</s>
<s>
Federated	B-Operating_System
search	I-Operating_System
may	O
have	O
to	O
restrict	O
itself	O
to	O
the	O
minimal	O
set	O
of	O
query	O
capabilities	O
that	O
are	O
common	O
to	O
all	O
federates	O
.	O
</s>
<s>
if	O
Google	B-Application
supports	I-Application
negation	O
and	O
quoted	O
phrases	O
,	O
but	O
science.gov	O
does	O
not	O
,	O
it	O
will	O
be	O
impossible	O
for	O
the	O
federated	B-Operating_System
search	I-Operating_System
to	O
support	O
negated	O
,	O
quoted	O
phrases	O
.	O
</s>
<s>
The	O
federated	B-Operating_System
search	I-Operating_System
must	O
decide	O
when	O
to	O
consider	O
a	O
federate	O
offline	O
,	O
or	O
wait	O
for	O
a	O
slow	O
response	O
.	O
</s>
<s>
Another	O
challenge	O
within	O
an	O
enterprise	O
is	O
HA/DR	O
(	O
high-availability	O
and	O
disaster	B-General_Concept
recovery	I-General_Concept
)	O
.	O
</s>
<s>
For	O
the	O
reasons	O
above	O
,	O
within	O
an	O
enterprise	O
,	O
a	O
data	B-Application
hub	I-Application
or	O
data	B-General_Concept
lake	I-General_Concept
may	O
be	O
preferable	O
,	O
or	O
a	O
hybrid	O
approach	O
.	O
</s>
<s>
Data	B-Application
hubs	I-Application
and	O
lakes	O
simplify	O
development	O
and	O
access	O
,	O
but	O
may	O
incur	O
some	O
time	O
lag	O
before	O
data	O
is	O
available	O
(	O
without	O
special	O
synchronizing	O
logic	O
)	O
.	O
</s>
