YaCy (speak: Jacky, like Blacky - publicized: Yet another CyberSpace) is a search machine, which works according to the Peer ton Peer principle - short P2P -. There is no central server, but all participants in it are equivalent.

Each Peer operator in the YaCy net can search, and if he liked to contribute all sides, which he visited over the YaCy Proxy index let to the index, by loose-sending a Webcrawler, or simply. If now any other Peer starts a search in the YaCy network, he can find all sides, which indicated other Peers, which is at the time of the search on-line. By the decentralized principle YaCy is fail safe.

Advantages & disadvantages

Advantages

• The global search machine developed with YaCy is practically fail safe, since a part of the network will be attainable always.
• The Internet users are independent by YaCy as search machine of companies, their Ranking (to possibly pay leave themselves the this) and their filtering (and censorship).
• The software is open SOURCE, under the GNU general Public License was published and is free.
• Since the indexation over the Proxy at the respective Client takes place, thus sides from the Deep Web or not public nets (e.g. i2p) can be indexed, which a Crawler cannot open.

Disadvantages

• Since YaCy for a retrieval query must contact many other Peers, the search lasts longer than with conventional search machines.
• For the moment only few Peers are present, so that fewer results are found than with large search machines.
• Since each Peer cannot store the entire index, it can come by loss or disconnection individual (large) Peers to implications of the overall index. This disadvantage is all the more strongly the less Peers actively at the YaCy network takes part.
• YaCy is based on Java and needs therefore components for the enterprise. Although YaCy stands under the GPL, it cannot be operated thus also excluding free software.

The program

The heart of the search machine is different than with other search machines not a central side, but a computer program, which is written in Java and runs therefore on nearly all operating systems.

Coupled with the P2P-System runs a pro XY server, which indicates most more far-reaching sides automatically. This does not take place however at sides, to which via GET or POST OFFICE further data (e.g. sides within a log in range) are handed over. Thus it is guaranteed that also really only publicly accessible data are indicated.

That access to search functionality is made by evenly the locally running server, in which over a used Suchmaske the search word or the search words is entered. The announcement of the results takes place here as used as HTML side.

Further characteristics

Further Yacy offers an additional Top level Domain "“.yacy"”, which can be achieved by means of all further YaCy Proxies and than normal web page is opened. Under these Domain has the user the possibility of depositing its own Website. Since the P2P-System must communicate anyway its IP address to its Peers, and also about a possible change to inform, the possibility is hereby in addition offered of developing at least for other YaCy users homepage without having problems with dynamic address assignment on the part of the Providers.

In addition the possibility is offered of releasing files on its local server on which other YaCy users have as desired access. Actually this is anyway already by the HTTP server the case, but additionally still another nice overview is indicated here.

In addition one has the possibility of sending to other YaCy users simple text messages (depending upon attitudes also with appendices of file). Thus a way is offered also here, spread and admitted - potentially more probably censored therefore it thus - media to avoid.

Additionally to it a Wiki is integrated in YaCy, which can be developed as local knowledge data base.

Technology

The program is based on a Web server, which at the same time cachingProxy is. Over the Web server one can access the user interface, in order to search or your own Peer administer. The Proxy divides its code with the Crawler, i.e. all visited sides, which are not personalisiert become automatically in the index seized. In addition the YaCy net offers own YaCy Domains, which is available over the Proxy.

Index distribution

Differently than with file exchange stock exchanges the result must be with a P2P-Suchmaschine immediately there. In order to ensure, YaCy uses a Distributed Hashtable (DHT). That is, that all seized URLs and words are sent to the Peers, their Peerhash to the appropriate Wordhash or Urlhash fits. With a search it functions exactly differently: It is looked for only on Peers, which can know their Hash after URLs for the word.

Thus only a fraction of the Peers must be contacted with the search, in order to get nevertheless good results.

Peertypen

YaCy differentiates four different kinds from Peers:

• Virgin. One cannot find this Peers, since a Virgin Peer does not have any contact to the net. Therefore one sees only if the Peer Virgin is.
• Junior. The Peer is behind a Firewall. Others can see it than junior or potential Peer, them recognize however only, when it announced itself the last mark to determine and has no possibilities whether it is still on-line.
• Senior

Literature

• R. Sietmann: Against the Monokultur. P2P-Strategien against the search machine monopolizing. in: c't, 2005/16, 25 July 2005, S.52-53 (on-line text)
• YaCy. in: HAZ: Article as pdf (107 KB)

Related links

• www.yacy.net - project side, on English
• www.yacy-websuche.de - project side, on German
• http://sourceforge.net/projects/yacy/ - project side for Developer
• Project summary to YaCy with Berlios

• http://yacy-websuche.de/index.php/yacybar.html - Firefox Toolbar downloaden

• http://www.yacy-forum.de/ (German forum and YaCy Entwicklerversionen)
• (English forum)
• http://www.deruwe.de/yacy.html announce (your homepage with one the which is running YaCy Webcrawler)
• http://www.yacy-websuche.de/wiki/index.php/De:Start (the official German Yacy Wiki)
• http://www.suma-lab.de:8080/ - search machine of a Nodes

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