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Search engine

In the context of the Internet, search engines usually refer to the World Wide Web and not other protocols or areas. Furthermore search engines mine data available in newsgroups, large databases, or open directories like DMOZ.org. Because the data collection is automated, they are distinguished from Web directories, which are maintained by people.

The vast majority of search engine are run by private companies using proprietary algorithms and closed databases, the most popular currently being Google (with MSN Search and Yahoo closely behind). There have been several attempts to create open-source search engines, among which are Htdig, Nutch, Egothor and OpenFTS. [1]

Table of contents

1 How search engines work 2 History 2.1 Google 3 Challenges faced by search engines 4 See also 5 External links

How search engines work

When a user comes to the search engine and makes a query, typically by giving key words, the engine looks up the 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.

The usefulness of a search engine depends on the relevance of the results it gives back. While there may be millions of Web pages 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.

History

Soon after, many search engines appeared and vied for popularity. These included WebCrawler, Hotbot, Excite, Infoseek, Inktomi, and AltaVista. In some ways they competed with popular directories such as Yahoo. Later, the directories integrated or added on search engine technology for greater functionality.

In 2002, Yahoo! acquired Inktomi and in 2003, Yahoo! aquired Overture, which owned AlltheWeb and Altavista. In 2004, Yahoo! launched it's own search engine based on the combined technologies of its acquisitions and providing a service that gave pre-eminence to the Web search engine over the directory.

Search engines were also known as some of the brightest stars in the Internet investing frenzy that occurred in the late 1990s. Several companies entered the market spectacularly, recording record gains during their initial public offerings.

Before the advent of the Web, there were search engines for other protocols or uses, such as the Archie search engine for anonymous FTP sites and the Veronica search engine for the Gopher protocol.

Osmar R. Zaïane's From Resource Discovery to Knowledge Discovery on the Internet details the history of search engine technology prior to the emergence of Google.

Recent additions to the list of search engines include a9.com, AlltheWeb, Ask Jeeves, Gigablast, Teoma, Wisenut, Kartoo, and Vivisimo.

Google

Researchers at NEC Research Institute claim to have improved upon Google's patented PageRank technology by using web crawlers to find "communities" of websites. Instead of ranking pages, this technology uses an algorithm that follows links on a webpage to find other pages that link back to the first one and so on from page to page. The algorithm "remembers" where it has been and indexes the number of cross-links and relates these into groupings. In this way virtual communities of webpages are found.

Challenges faced by search engines

• The web is growing much faster than any present-technology search engine can possibly index (see distributed crawling).
• Many web pages are updated frequently, which forces the search engine to revisit them periodically.
• The queries one can make are currently limited to searching for key words, which may results in many false positives.
• Dynamically generated sites, which may be slow or difficult to index, or may result in excessive results from a single site.
• Many dynamically generated sites are not indexable by search engines; this phenomenon is known as the invisible web.
• Some search engines do not order the results by relevance, but rather according to how much money the sites have paid them.
• Some sites use tricks to manipulate the search engine to display them as the first result returned for some keywords. This can lead to some search results being polluted, with more relevant links being pushed down in the result list.

• Search engine spammer
• History of the Internet
• List of search engines
• Data mining
• Metasearch engine

• Searchy - Internet Explorer Search Add-On
• On Search, the Series; Tim Bray; 2003 - A series of essays on search engine techniques.
• From Resource Discovery to Knowledge Discovery on the Internet (1998) (Recommendation: Click "PDF" in the upper right.)
• Search engine makes social calls (March 7, 2002; Nature.com)
• Understanding Search Engine Results
• Open, Distributed Web Search an article that discusses an open (source) approach to searching the web

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