Search Engine Realization

This section describes differences in the realization of the operation of the engine.

Index-based search engine
Metasearch

Federated Search Engines

Nowadays, the most important group are index-based search engines. This is a data structure that is used during a later search. Drawbacks are the expensive maintenance and storage of the index. The advantage is the acceleration of the search process. Most common form of this structure is an inverted index.

Metasearch engines send queries simultaneously to multiple index-based search engines and combine the individual results. As a result, the advantage is more data and simpler implementation, since no index should be reproached. Drawback is the relatively long duration of query processing.

Moreover, the ranking is by pure majority. The quality of the results will be reduced under certain circumstances on the quality of the worst search engine surveyed.
Meta search engines are particularly useful for infrequently occurring keywords.

Furthermore, there are hybrid forms. These have their own, often relatively small, index interview, than other search engines and then combine the individual results. So-called real-time search engines start the indexing process only after a request. Thus, the found pages are always up to date.

A relatively new approach is distributed search engines and Federated Search Engines. When a query is forwarded to a number of individual computers, each run its own search engine and merge the results.

Advantage is the high reliability due to the decentralization and – depending on the perspective – the inability to censor them centrally. It is difficult to solve the ranking however.

A special type of distributed search engine is based on the peer-to-peer principle of building a distributed index. In each of these one can understand the censorship of the Web Part, which defines the respective peer operators by simple local configuration.

The best known system was, besides a few mostly academic projects (such as Minerva) developed under the GNU GPL free software YaCy.