A web search engine is a software system that is designed to search for information on the World Wide Web. The search results are generally presented in a line of results often referred to as search engine results pages (SERPs). The information may be a mix of web pages, images, and other types of files. Some search engines also mine data available in databases or open directories. Unlike web directories, which are maintained only by human editors, search engines also maintain real-time information by running an algorithm on a web crawler.
Internet search engines themselves predate the debut of the Web in December 1990. The Whois user search dates back to 1982 [1] and the Knowbot Information Service multi-network user search was first implemented in 1989.[2] The first well documented search engine that searched content files, namely FTP files was Archie, which debuted on 10 September 1990.[citation needed]
Prior to September 1993 the World Wide Web was entirely indexed by hand. There was a list of webservers edited by Tim Berners-Lee and hosted on the CERN webserver. One historical snapshot of the list in 1992 remains,[3] but as more and more web servers went online the central list could no longer keep up. On the NCSA site, new servers were announced under the title "What's New!"[4]
The first tool used for searching content (as opposed to users) on the Internet was Archie.[5] The name stands for "archive" without the "v". It was created by Alan Emtage, Bill Heelan and J. Peter Deutsch, computer science students 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 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 periodically mirrored these pages and rewrote them into a standard format. This formed the basis for W3Catalog, the web's first primitive search engine, released on September 2, 1993.[6]
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 (created in December 1993[7] by Jonathon Fletcher) 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 it ran on,
its indexing and hence searching were limited to the titles and headings
found in the web pages the crawler encountered.
One of the first "all text" crawler-based search engines was WebCrawler,
which came out in 1994. Unlike its predecessors, it allowed users to
search for any word in any webpage, which has become the standard for
all major search engines since. It was also the first one 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 its full-text copies of web pages. Information seekers
could also browse the directory instead of doing a keyword-based search.
A search engine maintains the following processes in near real time:
Web search engines get their information by web crawling from site to site. The "spider" checks for the standard filename robots.txt, addressed to it, before sending certain information back to be indexed depending on many factors, such as the titles, page content, JavaScript, Cascading Style Sheets (CSS), headings, as evidenced by the standard HTML markup of the informational content, or its metadata in HTML meta tags.
Indexing means associating words and other definable tokens found on
web pages to their domain names and HTML-based fields. The associations
are made in a public database, made available for web search queries. A
query from a user can be a single word. The index helps find information
relating to the query as quickly as possible.[14]
Some of the techniques for indexing, and cacheing are trade secrets, whereas web crawling is a straightforward process of visiting all sites on a systematic basis.
Between visits by the spider, the cached version of page (some
or all the content needed to render it) stored in the search engine
working memory is quickly sent to an inquirer. If a visit is overdue,
the search engine can just act as a web proxy instead. In this case the page may differ from the search terms indexed.[14]
The cached page holds the appearance of the version whose words were
indexed, so a cached version of a page can be useful to the web site
when the actual page has been lost, but this problem is also considered a
mild form of linkrot.
Typically when a user enters a query into a search engine it is a few keywords.[15] The index
already has the names of the sites containing the keywords, and these
are instantly obtained from the index. The real processing load is in
generating the web pages that are the search results list: Every page in
the entire list must be weighted according to information in the indexes.[14] Then the top search result item requires the lookup, reconstruction, and markup of the snippets
showing the context of the keywords matched. These are only part of the
processing each search results web page requires, and further pages
(next to the top) require more of this post processing.
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