A search engine (SuM), Search Engine(SE), is a central facility of the World Wide Web(WWW), which can be used to search for information and documents on the Internet. The Internet user enters his search query into the search engine, which then searches its extracted databases for corresponding entries. Searches are also limited by weightings and for the number of search results that the search engine user wants.
Search engines use robots, crawlers or spiders for searches. These automatically running search engines scan the web for new and updated web pages, follow the links, collect the relevant information based on the keywords from the tags and metatags and provide it to the search engine. From the data collected by the crawlers, certain features are extracted, reducing the amount of data. The extracted features are indexed and sorted. In the process, the search engines catalog the respective dataset according to a predefined hierarchy.
The result lists, the Search Engine Result Pages( SERP), are stored in the search engine database, analyzed, indexed and hyperlinked. In order to optimize efficiency and speed in the search results, various search engines analyze the number of links on a website.
Since search engines are of central importance for many website operators, they work with sophisticated procedures so that their offers are recognized by visitors and generate sales. All these procedures are part of search engine marketing( SEM). Directly related to this is the improved positioning of one's own web pages in the search results. This technique is called search engine optimization( SEO).
The universal search engines are called horizontal search engines. In addition, there are the vertical search engines specialized in certain subject areas or target groups. There are many horizontal search engines such as AltaVista, Google, Bing, Flipper, Infoseek, Meta-Searcher, Qwant, Lycos, Open Text, Feedster, DuckDuckGo, Yahoo, Cuil and others. Higher- level search engines that submit queries to multiple search engines and evaluate them according to their own algorithms are called meta-searchengines, and specialized search engines that recommend products or articles to prospective customers are called recommendation engines.
In addition to Internet search engines, there is Watson, an offline search engine for databases that works with semantic queries.