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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 Intranet s, ''personal search engines'', which search individual personal computers, and ''mobile search engines''. However, while different selection and relevance criteria may apply in different environments, the user will probably perceive little difference between operations in these. Some search engines also mine data available in newsgroups, large databases, or open directories like DMOZ.org . Unlike Web Directories , which are maintained by human editors, search engines operate algorithmically. Most web sites which call themselves search engines are actually front ends to search engines owned by other companies. HISTORY The very first tool used for searching on the Internet was called "Archie" . (The name stands for "archive" without the "v", not the Character from the 'Archie' comic book series). 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. While Archie indexed computer files, "Gopher" indexed plain text documents. Gopher was created in 1991 by Mark McCahill at the University Of Minnesota . (The program was named after the school's Mascot ). Because these were text files, most of the Gopher sites became Web sites 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. 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 web page, 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, recording record gains during their Initial Public Offering s. Some have taken down their public search engine, and are marketing enterprise-only editions, such as Northern Light. Before the advent of the Web, there were search engines for other Blogs . Around 2001, the Google search engine rose to prominence. Its success was based in part on the concept of Link Popularity and PageRank . How many other web sites and web pages 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 web sites link to each found page. Google's minimalist User Interface was 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. The algorithm "remembers" where it has been and indexes the number of Cross-link s 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 Dr. Jon Kleinberg and his team while working on the CLEVER project at IBM's Almaden research lab. Google is currently the most popular search engine. Yahoo! Search 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 web site 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 , 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 . A new next generation search engine launched by Microsoft LIVE.COM promises the best search experience ever made
The other large (self described) search engines tend to be "portals" that merely show the results from another company's search engine (like MSN Search used to do). The other "true" search engines (those that provide their own results), like Gigablast , have vastly less market presence than the big three. However, since site usage is proprietary information, it's often difficult to determine which sites are most popular. CHALLENGES FACED BY SEARCH ENGINES
HOW SEARCH ENGINES WORK A search engine operates, in the following order # Web Crawling # Indexing # Searching Web search engines work by storing information about a large number of Web Page s, 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 is 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 some store every word of every page it finds, such as AltaVista . 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 web page. 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 Word s, 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 you 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 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. The vast majority of search engines are run by private companies using proprietary algorithms and closed databases, the most popular currently being , Nutch , Senas , Egothor , OpenFTS , DataparkSearch and many others . STORAGE COSTS AND CRAWLING TIME A modern search engine can operate with stunningly modest storage requirements. Assuming a 500GB drive costs $100 USD (2006 prices), and that an average web page compresses to less than 10K, 10B pages would compress to 100TB, thus using 200 Hard Drives and cost around $20K. If we kept 4 drives per server, we would need no more than 50 servers to store these 10B pages, which at $250/computer would cost under $12.5K. Thus it is possible to have 10B pages held on a Server Farm with no more than $35K of hardware. Most search engines, in order to serve millions of search queries, serve ads and process the crawl have considerably more resources than this, and allow for significant redundancy to handle disruptions in service. Crawling 10B pages with 100 machines crawling at 100 pages/second would take 1M seconds, or 11.6 days. Most search engines crawl a small fraction of the web (10-20% pages) at around this frequency or better, but also crawl dynamic web sites (e.g. News Site s and Blog s) at a much higher frequency. GEOSPATIALLY ENABLED SEARCH ENGINES A recent enhancement to search engine technology is the addition of Web Service to allow deep integration into existing applications. MetaCarta also provides an extension for desktop GIS software such as ESRI 's ArcGIS , to allow analysts to interactively query the search engine and retrieve documents in an advanced geospatial and analytical context. SEE ALSO
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