<s>
A	O
client	B-Architecture
–	I-Architecture
queue	I-Architecture
–	I-Architecture
client	I-Architecture
or	O
passive	O
queue	B-Application
system	O
is	O
a	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
computer	B-Architecture
network	I-Architecture
in	O
which	O
the	O
server	B-Application
is	O
a	O
data	O
queue	B-Application
for	O
the	O
clients	B-Protocol
.	O
</s>
<s>
Instead	O
of	O
communicating	O
with	O
each	O
other	O
directly	O
,	O
clients	B-Protocol
exchange	O
data	O
with	O
one	O
another	O
by	O
storing	O
it	O
in	O
a	O
repository	O
(	O
the	O
queue	B-Application
)	O
on	O
a	O
server	B-Application
.	O
</s>
<s>
Like	O
peer-to-peer	O
,	O
the	O
client	B-Architecture
–	I-Architecture
queue	I-Architecture
–	I-Architecture
client	I-Architecture
system	O
empowers	O
hosts	O
on	O
the	O
network	O
to	O
serve	O
data	O
to	O
other	O
hosts	O
.	O
</s>
<s>
Web	B-Application
crawlers	I-Application
on	O
different	O
hosts	O
need	O
to	O
query	O
each	O
other	O
to	O
synchronize	O
an	O
indexed	O
URI	B-Protocol
.	O
</s>
<s>
Whereas	O
one	O
approach	O
is	O
to	O
program	O
each	O
crawler	O
to	O
receive	O
and	O
respond	O
to	O
such	O
queries	O
,	O
the	O
client	B-Architecture
–	I-Architecture
queue	I-Architecture
–	I-Architecture
client	I-Architecture
approach	O
is	O
to	O
store	O
the	O
indexed	O
content	O
from	O
both	O
crawlers	O
in	O
a	O
passive	O
queue	B-Application
,	O
such	O
as	O
a	O
relational	B-Application
database	I-Application
,	O
on	O
another	O
host	B-Device
.	O
</s>
<s>
Both	O
web	B-Application
crawlers	I-Application
read	O
and	O
write	O
to	O
the	O
database	O
,	O
but	O
never	O
communicate	O
with	O
each	O
other	O
.	O
</s>
