Search engine From Wikipedia, the free encyclopedia Jump to: navigation, search This article is on the general topic; for a specific search engine, see List of search engines. Google search is the world's most popular search engine. Google search is the world's most popular search engine. A search engine is an information retrieval system designed to help find information stored on a computer system, such as on the World Wide Web, inside a corporate or proprietary network, or in a personal computer. The search engine allows one to ask for content meeting specific criteria (typically those containing a given word or phrase) and retrieves a list of items that match those criteria. This list is often sorted with respect to some measure of relevance of the results. Search engines use regularly updated indexes to operate quickly and efficiently. Without further qualification, search engine usually refers to a Web search engine, which searches for information on the public Web. Other kinds of search engine are enterprise search engines, which search on intranets, personal search engines, and mobile search engines. Different selection and relevance criteria may apply in different environments, or for different uses. 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 algorthmic and human input. Contents [hide] * 1 History o 1.1 Google o 1.2 Yahoo! Search o 1.3 Microsoft o 1.4 Baidu * 2 Challenges faced by search engines * 3 How search engines work * 4 Storage costs and crawling time * 5 Geospatially enabled search engines * 6 Vertical Search Engines o 6.1 Category-focused vertical search engines o 6.2 Media-focused search engines * 7 Charity search * 8 Social search * 9 See also * 10 Notes * 11 References * 12 External links History The very first tool used for searching on the Internet was Archie.[1] The name stands for "archive" without the "v". It was created in 1990 by Alan Emtage, a student at McGill University in Montreal. The program downloaded the directory listings of all the files located on public anonymous FTP (File Transfer Protocol) sites, creating a searchable database of filenames; however, Archie could not search by file contents. While Archie indexed computer files, Gopher indexed plain text documents. Gopher was created in 1991 by Mark McCahill at the University of Minnesota: Gopher was named after the school's mascot.[1] Because these were text files, most of the Gopher sites became websites after the creation of the World Wide Web. Two other programs, Veronica and Jughead, searched the files stored in Gopher index systems. Veronica (Very Easy Rodent-Oriented Net-wide Index to Computerized Archives) provided a keyword search of most Gopher menu titles in the entire Gopher listings. Jughead (Jonzy's Universal Gopher Hierarchy Excavation And Display) was a tool for obtaining menu information from various Gopher servers. While the name of the search engine "Archie" was not a reference to the Archie comic book series, "Veronica" and "Jughead" are characters in the series, thus referencing their predecessor. 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 1996 Dogpile Launch Inktomi Founded Ask Jeeves Founded 1997 Northern Light Launch 1998 Google Launch 1999 AlltheWeb Launch Teoma Founded Vivisimo Founded 2000 Baidu Founded 2003 Info.com Launch 2004 Yahoo! Search Final launch 2005 MSN Search Final launch Ask.com Launch 2006 wikiseek Founded Quaero Founded Ask.com Launch Windows Live Search Launch ChaCha Beta Launch Quintura Beta Launch wikiseek Beta Launch 2007 wikiseek Launched The first Web search engine was Wandex, a now-defunct index collected by the World Wide Web Wanderer, a web crawler developed by Matthew Gray at MIT in 1993. Another very early search engine, Aliweb, also appeared in 1993, and still runs today. The first "full text" crawler-based search engine was WebCrawler, which came out in 1994. Unlike its predecessors, it let users search for any word in any webpage, which became the standard for all major search engines since. It was also the first one to be widely known by the public. Also in 1994 Lycos (which started at Carnegie Mellon University) came out, and became a major commercial endeavor. Soon after, many search engines appeared and vied for popularity. These included Excite, Infoseek, Inktomi, Northern Light, 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. 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, receiving record gains during their initial public offerings. Some have taken down their public search engine, and are marketing enterprise-only editions, such as Northern Light. Google Around 2001, the Google search engine rose to prominence. Its success was based in part on the concept of link popularity and PageRank. The number of other websites and webpages that link to a given page is taken into consideration with PageRank, on the premise that good or desirable pages are linked to more than others. The PageRank of linking pages and the number of links on these pages contribute to the PageRank of the linked page. This makes it possible for Google to order its results by how many websites link to each found page. Google's minimalist user interface is very popular with users, and has since spawned a number of imitators. Google and most other web engines utilize not only PageRank but more than 150 criteria to determine relevancy.[2] The algorithm "remembers" where it has been and indexes the number of cross-links and relates these into groupings. PageRank is based on citation analysis that was developed in the 1950s by Eugene Garfield at the University of Pennsylvania. Google's founders cite Garfield's work in their original paper. In this way virtual communities of webpages are found. Teoma's search technology uses a communities approach in its ranking algorithm. NEC Research Institute has worked on similar technology. Web link analysis was first developed by Jon Kleinberg and his team while working on the CLEVER project at IBM's Almaden Research Center. Google is currently the most popular search engine.[3] Yahoo! Search The two founders of Yahoo!, David Filo and Jerry Yang, Ph.D. candidates in Electrical Engineering at Stanford University, started their guide in a campus trailer in February 1994 as a way to keep track of their personal interests on the Internet. Before long they were spending more time on their home-brewed lists of favourite links than on their doctoral dissertations. Eventually, Jerry and David's lists became too long and unwieldy, and they broke them out into categories. When the categories became too full, they developed subcategories ... and the core concept behind Yahoo! was born. In 2002, Yahoo! acquired Inktomi and in 2003, Yahoo! acquired Overture, which owned AlltheWeb and AltaVista. Despite owning its own search engine, Yahoo! initially kept using Google to provide its users with search results on its main website Yahoo.com. However, in 2004, Yahoo! launched its 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. Microsoft The most recent major search engine is MSN Search (evolved into Windows Live Search), owned by Microsoft, which previously relied on others for its search engine listings. In 2004 it debuted a beta version of its own results, powered by its own web crawler (called msnbot). In early 2005 it started showing its own results live. This was barely noticed by average users unaware of where results come from, but was a huge development for many webmasters, who seek inclusion in the major search engines. At the same time, Microsoft ceased using results from Inktomi, now owned by Yahoo!. In 2006, Microsoft migrated to a new search platform - Windows Live Search, retiring the "MSN Search" name in the process. Baidu Due to the difference between hanzi and the Roman alphabet, the Chinese search market did not boom until the introduction of Baidu in 2000.[citation needed] Challenges faced by search engines * The Web is growing much faster than any present-technology search engine can possibly index (see distributed web crawling). In 2006, some users found major search-engines became slower to index new webpages.[4] * Many webpages 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 result in many false positives, especially using the default whole-page search. Better results might be achieved by using a proximity-search option with a search-bracket to limit matches within a paragraph or phrase, rather than matching random words scattered across large pages. Another alternative is using human operators to do the researching for the user with organic search engines. * Dynamically generated sites may be slow or difficult to index, or may result in excessive results, perhaps generating 500 times more webpages than average. Example: for a dynamic webpage which changes content based on entries inserted from a database, a search-engine might be requested to index 50,000 static webpages for 50,000 different parameter values passed to that dynamic webpage.[5] * Many dynamically generated websites are not indexable by search engines; this phenomenon is known as the invisible web. There are search engines that specialize in crawling the invisible web by crawling sites that have dynamic content, require forms to be filled out, or are password protected. * Relevancy: sometimes the engine can't get what the person is looking for. * Some search-engines do not rank results by relevance, but by the amount of money the matching websites pay. * In 2006, hundreds of generated websites used tricks to manipulate a search-engine to display them in the higher results for numerous keywords. This can lead to some search results being polluted with linkspam or bait-and-switch pages which contain little or no information about the matching phrases. The more relevant webpages are pushed further down in the results list, perhaps by 500 entries or more.[6] * Secure pages (content hosted on HTTPS URLs) pose a challenge for crawlers which either can't browse the content for technical reasons or won't index it for privacy reasons. How search engines work A search engine operates, in the following order 1. Web crawling 2. Indexing 3. Searching Web search engines work by storing information about a large number of 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 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. Most search engines support the use of the boolean terms AND, OR and NOT to further specify the search query. An advanced feature is 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 everytime 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.[citation needed]