<s>
YaCy	B-Application
(	O
pronounced	O
“	O
ya	O
see	O
”	O
)	O
is	O
a	O
free	B-Application
distributed	B-Application
search	I-Application
engine	I-Application
,	O
built	O
on	O
the	O
principles	O
of	O
peer-to-peer	O
(	O
P2P	O
)	O
networks	O
created	O
by	O
Michael	O
Christen	O
in	O
2003	O
.	O
</s>
<s>
The	O
engine	O
is	O
written	O
in	O
Java	B-Language
and	O
distributed	O
on	O
several	O
hundred	O
computers	O
,	O
,	O
so-called	O
YaCy-peers	O
.	O
</s>
<s>
Each	O
YaCy-peer	O
independently	O
crawls	O
through	O
the	O
Internet	O
,	O
analyzes	O
and	O
indexes	O
found	O
web	O
pages	O
,	O
and	O
stores	O
indexing	O
results	O
in	O
a	O
common	O
database	O
(	O
so-called	O
index	O
)	O
which	O
is	O
shared	O
with	O
other	O
YaCy-peers	O
using	O
principles	O
of	O
peer-to-peer	O
.	O
</s>
<s>
It	O
is	O
a	O
search	B-Application
engine	I-Application
that	O
everyone	O
can	O
use	O
to	O
build	O
a	O
search	B-Application
portal	I-Application
for	O
their	O
intranet	O
and	O
to	O
help	O
search	O
the	O
public	O
internet	O
clearly	O
.	O
</s>
<s>
Compared	O
to	O
semi-distributed	O
search	O
engines	O
,	O
the	O
YaCy-network	O
has	O
a	O
distributed	O
architecture	O
.	O
</s>
<s>
All	O
YaCy-peers	O
are	O
equal	O
and	O
no	O
central	O
server	B-Application
exists	O
.	O
</s>
<s>
It	O
can	O
be	O
run	O
either	O
in	O
a	O
crawling	B-Application
mode	O
or	O
as	O
a	O
local	O
proxy	B-Application
server	I-Application
,	O
indexing	O
web	O
pages	O
visited	O
by	O
the	O
person	O
running	O
YaCy	B-Application
on	O
their	O
computer	O
.	O
</s>
<s>
Access	O
to	O
the	O
search	O
functions	O
is	O
made	O
by	O
a	O
locally	O
run	O
web	O
server	B-Application
which	O
provides	O
a	O
search	O
box	O
to	O
enter	O
search	O
terms	O
,	O
and	O
returns	O
search	B-Application
results	I-Application
in	O
a	O
similar	O
format	O
to	O
other	O
popular	O
search	B-Application
engines	I-Application
.	O
</s>
<s>
YaCy	B-Application
search	B-Application
engine	I-Application
is	O
based	O
on	O
four	O
elements	O
:	O
</s>
<s>
Crawler	O
A	O
search	B-Application
robot	I-Application
that	O
traverses	O
between	O
web	O
pages	O
,	O
analyzing	O
their	O
content	O
.	O
</s>
<s>
Indexer	O
It	O
creates	O
a	O
reverse	B-Algorithm
word	I-Algorithm
index	I-Algorithm
(	O
RWI	O
)	O
,	O
i.e.	O
,	O
each	O
word	O
from	O
the	O
RWI	O
has	O
its	O
own	O
list	O
of	O
relevant	O
URLs	O
and	O
ranking	O
information	O
.	O
</s>
<s>
Search	O
and	O
administration	O
interface	O
Made	O
as	O
a	O
web	O
interface	O
provided	O
by	O
a	O
local	O
HTTP	B-Protocol
servlet	O
with	O
servlet	O
engine	O
.	O
</s>
<s>
Data	O
storage	O
Used	O
to	O
store	O
the	O
reverse	B-Algorithm
word	I-Algorithm
index	I-Algorithm
database	O
utilizing	O
a	O
distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
.	O
</s>
<s>
YaCy	B-Application
is	O
a	O
complete	O
search	O
appliance	B-Application
with	O
user	O
interface	O
,	O
index	O
,	O
administration	O
and	O
monitoring	O
.	O
</s>
<s>
YaCy	B-Application
harvests	O
web	O
pages	O
with	O
a	O
web	B-Application
crawler	I-Application
.	O
</s>
<s>
A	O
search	O
is	O
started	O
,	O
then	O
the	O
local	O
index	O
contributes	O
together	O
with	O
a	O
global	O
search	O
index	O
from	O
peers	O
in	O
the	O
YaCy	B-Application
search	O
network	O
.	O
</s>
<s>
The	O
YaCy	B-Application
Grid	O
is	O
a	O
second-generation	O
implementation	O
of	O
the	O
YaCy	B-Application
peer-to-peer	O
search	O
.	O
</s>
<s>
A	O
YaCy	B-Application
Grid	O
installation	O
consists	O
of	O
microservices	O
that	O
communicate	O
using	O
the	O
Master	O
Connect	O
Program	O
(	O
MCP	O
)	O
.	O
</s>
<s>
The	O
YaCy	B-Application
Parser	O
is	O
a	O
microservice	O
that	O
can	O
be	O
deployed	O
using	O
Docker	B-Language
.	O
</s>
<s>
YaCy	B-Application
uses	O
a	O
combination	O
of	O
techniques	O
for	O
the	O
networking	O
,	O
administration	O
,	O
and	O
maintenance	O
of	O
indexing	O
the	O
search	B-Application
engine	I-Application
,	O
including	O
blacklisting	O
,	O
moderation	O
,	O
and	O
communication	O
with	O
the	O
community	O
.	O
</s>
<s>
Here	O
is	O
how	O
YaCy	B-Application
performs	O
these	O
operations	O
:	O
</s>
<s>
YaCy	B-Application
is	O
available	O
in	O
packages	O
for	O
Linux	O
,	O
Windows	O
,	O
Macintosh	O
and	O
also	O
as	O
a	O
Docker	B-Language
image	O
.	O
</s>
<s>
YaCy	B-Application
can	O
also	O
be	O
installed	O
on	O
any	O
other	O
operating	O
system	O
either	O
by	O
manually	O
compiling	O
it	O
,	O
or	O
using	O
a	O
tarball	B-Application
.	O
</s>
<s>
YaCy	B-Application
requires	O
Java	B-Language
8	O
,	O
OpenJDK	O
8	O
is	O
recommended	O
.	O
</s>
