Web search engine
From Wikipedia, the free encyclopedia
A
web search engine is designed to search for information on the
World Wide Web. The search results are generally presented in a list of results and are often called
hits. The information may consist of
web pages, images, information and other types of files. Some search engines also
mine data available in
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.
[edit] History
During the early development of the web, there was a list of
webservers edited by
Tim Berners-Lee and hosted on the
CERN webserver. One historical snapshot from 1992 remains.
[1] As more webservers went online the central list could not keep up. On the
NCSA site new servers were announced under the title "What's New!"
[2]
The very first tool used for searching on the Internet was
Archie.
[3] The name stands for "archive" without the "v." It was created in 1990 by
Alan Emtage, a computer science 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 file names; however, Archie did not index the contents of these sites since the amount of data was so limited it could be readily searched manually.
The rise of
Gopher (created in 1991 by
Mark McCahill at the
University of Minnesota) led to two new search programs,
Veronica and
Jughead. Like Archie, they searched the file names and titles 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 specific 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.
In the summer of 1993, no search engine existed yet for the web, though numerous specialized catalogues were maintained by hand.
Oscar Nierstrasz at the
University of Geneva wrote a series of
Perl scripts that would periodically mirror these pages and rewrite them into a standard format which formed the basis for
W3Catalog, the web's first primitive search engine, released on September 2, 1993
[4].
In June 1993, Matthew Gray, then at
MIT, produced what was probably the first
web robot, the
Perl-based
World Wide Web Wanderer, and used it to generate an index called 'Wandex'. The purpose of the Wanderer was to measure the size of the World Wide Web, which it did until late 1995. The web's second search engine
Aliweb appeared in November 1993. Aliweb did not use a
web robot, but instead depended on being notified by website administrators of the existence at each site of an index file in a particular format.
JumpStation (released in December 1993
[5]) used a
web robot to find web pages and to build its index, and used a
web form as the interface to its query program. It was thus the first WWW resource-discovery tool to combine the three essential features of a web search engine (crawling, indexing, and searching) as described below. Because of the limited resources available on the platform on which it ran, its indexing and hence searching were limited to the titles and headings found in the web pages the crawler encountered.
One of the first "full text" crawler-based search engines was
WebCrawler, which came out in 1994. Unlike its predecessors, it let users search for any word in any webpage, which has become 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) was launched and became a major commercial endeavor.
Soon after, many search engines appeared and vied for popularity. These included
Magellan,
Excite,
Infoseek,
Inktomi,
Northern Light, and
AltaVista.
Yahoo! was among the most popular ways for people to find web pages of interest, but its search function operated on its
web directory, rather than full-text copies of web pages. Information seekers could also browse the directory instead of doing a keyword-based search.
In 1996,
Netscape was looking to give a single search engine an exclusive deal to be their featured search engine. There was so much interest that instead a deal was struck with Netscape by five of the major search engines, where for $5Million per year each search engine would be in a rotation on the Netscape search engine page. The five engines were Yahoo!, Magellan, Lycos, Infoseek, and Excite.
[6][7]
Search engines were also known as some of the brightest stars in the Internet investing frenzy that occurred in the late 1990s.
[8] 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. Many search engine companies were caught up in the
dot-com bubble, a speculation-driven market boom that peaked in 1999 and ended in 2001.
Around 2000, the
Google search engine rose to prominence.
[citation needed] The company achieved better results for many searches with an innovation called
PageRank. This
iterative algorithm ranks web pages based on the number and PageRank of other web sites and pages that link there, on the premise that good or desirable pages are linked to more than others. Google also maintained a minimalist interface to its search engine. In contrast, many of its competitors embedded a search engine in a
web portal.
By 2000, Yahoo was providing search services based on Inktomi's search engine. Yahoo! acquired Inktomi in 2002, and
Overture (which owned
AlltheWeb and AltaVista) in 2003. Yahoo! switched to Google's search engine until 2004, when it launched its own search engine based on the combined technologies of its acquisitions.
Microsoft first launched MSN Search in the fall of 1998 using search results from Inktomi. In early 1999 the site began to display listings from
Looksmart blended with results from Inktomi except for a short time in 1999 when results from AltaVista were used instead. In 2004,
Microsoft began a transition to its own search technology, powered by its own
web crawler (called
msnbot).
Microsoft's rebranded search engine,
Bing, was launched on June 1, 2009. On July 29, 2009, Yahoo! and Microsoft finalized a deal in which
Yahoo! Search would be powered by Microsoft Bing technology.
According to Hitbox,
[9] Google's worldwide popularity peaked at 82.7% in December, 2008. July 2009 rankings showed Google (78.4%) losing traffic to
Baidu (8.87%), and Bing (3.17%). The market share of Yahoo! Search (7.16%) and
AOL (0.6%) were also declining.
In the United States, Google held a 63.2% market share in May 2009, according to Nielsen NetRatings.
[10] In the
People's Republic of China, Baidu held a 61.6% market share for web search in July 2009.
[11]
[edit] How web search engines work
A search engine operates, in the following order
- Web crawling
- Indexing
- Searching
Web search engines work by storing information about many web pages, which they retrieve from the html itself. These pages are retrieved by a
Web crawler (sometimes also known as a spider) — an automated Web browser which follows every link on the site. 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. A query can be a single word. The purpose of an index is to allow information to be found as quickly as possible. 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. The index is built from the information stored with the data and the method by which the information is indexed. Unfortunately, there are currently no known public search engines that allow documents to be searched by date. Most search engines support the use of the
boolean operators AND, OR and NOT to further specify the
search query. Boolean operators are for literal searches that allow the user to refine and extend the terms of the search. The engine looks for the words or phrases exactly as entered. Some search engines provide an advanced feature called
proximity search which allows users to define the distance between keywords. There is also concept-based searching where the research involves using statistical analysis on pages containing the words or phrases you search for. As well, natural language queries allow the user to type a question in the same form one would ask it to a human. A site like this would be ask.com.
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. There are two main types of search engine that have evolved: one is a system of predefined and hierarchically ordered keywords that humans have programmed extensively. The other is a system that generates an "
inverted index" by analyzing texts it locates. This second form relies much more heavily on the computer itself to do the bulk of the work.
Most Web search engines are commercial ventures supported by
advertising revenue and, as a result, some employ the 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.
