A Web search engine is a search engine designed to search for information on the World Wide Web. Information may consist of web pages, images and other types of files.
Some search engines also mine data available in newsgroups, databases, or open directories. Unlike Web directories, which are maintained by human editors, search engines operate algorithmically or are a mixture of algorithmic and human input.
| Timeline | ||||
|---|---|---|---|---|
| Note: "Launch" refers only to web availability of original crawl-based web search engine results. | ||||
| Year | Engine | Event | ||
| 1993 | Aliweb | Launch | ||
| 1994 | WebCrawler | Launch | ||
| Infoseek | Launch | |||
| Lycos | Launch | |||
| 1995 | AltaVista | Launch (part of DEC) | ||
| Excite | Launch | |||
| SAPO | Launch | |||
| 1996 | Dogpile | Launch | ||
| Inktomi | Founded | |||
| HotBot | Founded | |||
| Ask Jeeves | Founded | |||
| 1997 | Northern Light | Launch | ||
| 1998 | Launch | |||
| 1999 | AlltheWeb | Launch | ||
| Naver | Launch | |||
| Teoma | Founded | |||
| Vivisimo | Founded | |||
| 2000 | Baidu | Founded | ||
| 2003 | Info.com | Launch | ||
| 2004 | Yahoo! Search | Final launch | ||
| A9.com | Launch | |||
| 2005 | MSN Search | Final launch | ||
| Ask.com | Launch | |||
| GoodSearch | Launch | |||
| 2006 | wikiseek | Founded | ||
| Quaero | Founded | |||
| Ask.com | Launch | |||
| Live Search | Launch | |||
| ChaCha | Beta Launch | |||
| Guruji.com | Beta Launch | |||
| 2007 | itah.com | Launched | ||
| wikiseek | Launched | |||
| AskWiki | Launched | |||
As of late 2007, Google was by far the most popular Web search engine worldwide.A number of country-specific search engine companies have become prominent; for example Baidu is the most popular search engine in the People's Republic of China.
Current market share
| Most popular search engines worldwide, Dec. 2007 | ||
|---|---|---|
| Company | Millions of searches | Relative market share |
| 28,454 | 46.47% | |
| Yahoo! | 10,505 | 17.16% |
| Baidu | 8,428 | 13.76% |
| Microsoft | 7,880 | 12.87% |
| NHN | 2,882 | 4.71% |
| eBay | 2,428 | 3.9% |
| Time Warner (includes AOL) | 1,062 | 1.6% |
| Ask.com and related | 728 | 1.1% |
| Yandex | 566 | 0.9% |
| Alibaba.com | 531 | 0.8% |
| Total | 61,221 | 100.0% |
HOW SEARCH ENGINE WORKS
A search engine operates, in the following order
Web search engines work by storing information about many web pages, which they retrieve from the WWW itself. These pages are retrieved by a Web crawler (sometimes also known as a spider) — an automated Web browser which follows every link it sees. Exclusions can be made by the use of robots.txt. The contents of each page are then analyzed to determine how it should be indexed (for example, words are extracted from the titles, headings, or special fields called meta tags). Data about web pages are stored in an index database for use in later queries. Some search engines, such as Google, store all or part of the source page (referred to as a cache) as well as information about the web pages, whereas others, such as AltaVista, store every word of every page they find. This cached page always holds the actual search text since it is the one that was actually indexed, so it can be very useful when the content of the current page has been updated and the search terms are no longer in it. This problem might be considered to be a mild form of linkrot, and Google's handling of it increases usability by satisfying user expectations that the search terms will be on the returned webpage. This satisfies the principle of least astonishment since the user normally expects the search terms to be on the returned pages. Increased search relevance makes these cached pages very useful, even beyond the fact that they may contain data that may no longer be available elsewhere.
When a user enters a query into a search engine (typically by using key words), the engine examines its index and provides a listing of best-matching web pages according to its criteria, usually with a short summary containing the document's title and sometimes parts of the text. Most search engines support the use of the boolean operators AND, OR and NOT to further specify the search query. Some search engines provide an advanced feature called proximity search which allows users to define the distance between keywords.
The usefulness of a search engine depends on the relevance of the result set it gives back. While there may be millions of webpages that include a particular word or phrase, some pages may be more relevant, popular, or authoritative than others. Most search engines employ methods to rank the results to provide the "best" results first. How a search engine decides which pages are the best matches, and what order the results should be shown in, varies widely from one engine to another. The methods also change over time as Internet usage changes and new techniques evolve.
Most Web search engines are commercial ventures supported by advertising revenue and, as a result, some employ the controversial practice of allowing advertisers to pay money to have their listings ranked higher in search results. Those search engines which do not accept money for their search engine results make money by running search related ads alongside the regular search engine results. The search engines make money every time someone clicks on one of these ads.
The vast majority of search engines are run by private companies using proprietary algorithms and closed databases, though some are open source.
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