A
search engine is an information retrieval system designed
to help find information stored on a computer system.
Search engines help to minimize the time required
to find information and the amount of information
which must be consulted, akin to other techniques
for managing information overload.
The
most public, visible form of a search engine is a
Web search engine which searches for information on
the World Wide Web. Of course, it is precisely search
engine technology that allowed Wikipedia to revolutionize
information seeking, with the creation of an online,
searchable encyclopedia. The popular web browser Firefox
has an add-on that installs the Wikipedia search engine
directly into its Search Bar.
How
search engines work
Search
engines provide an interface to a group of items that
enables users to specify criteria about an item of
interest and have the engine find the matching items.
The criteria are referred to as a search query. In
the case of text search engines, the search query
is typically expressed as a set of words that identify
the desired concept that one or more documents may
contain. There are several styles of search query
syntax that vary in strictness. It can also switch
names with in the search engines from previous sites.
Where as some text search engines require users to
enter two or three words separated by white space,
other search engines may enable users to specify entire
documents, pictures, sounds, and various forms of
natural language. Some search engines apply improvements
to search queries to increase the likelihood of providing
a quality set of items through a process known as
query expansion.
The
list of items that meet the criteria specified by
the query is typically sorted, or ranked, in some
regard so as to place the most relevant items first.
Ranking items by relevance (from highest to lowest)
reduces the time required to find the desired information.
Probabilistic search engines rank items based on measures
of similarity (between each item and the query, typically
on a scale of 1 to 0, 1 being most similar) and sometimes
popularity or authority (see Bibliometrics) or use
relevance feedback. Boolean search engines typically
only return items which match exactly without regard
to order, although the term boolean search engine
may simply refer to the use of boolean-style syntax
(the use of operators AND, OR, NOT, and XOR) in a
probabilistic context.
To
provide a set of matching items that are sorted according
to some criteria quickly, a search engine will typically
collect metadata about the group of items under consideration
beforehand through a process referred to as indexing.
The index typically requires a smaller amount of computer
storage, which is why some search engines only store
the indexed information and not the full content of
each item, and instead provide a method of navigating
to the items in the search engine result page. Alternatively,
the search engine may store a copy of each item in
a cache so that users can see the state of the item
at the time it was indexed or for archive purposes
or to make repetitive processes work more efficiently
and quickly.
Other
types of search engines do not store an index. Crawler,
or spider type search engines (a.k.a. real-time search
engines) may collect and assess items at the time
of the search query, dynamically considering additional
items based on the contents of a starting item (known
as a seed, or seed URL in the case of an Internet
crawler). Meta search engines do not store an index
nor a cache and instead simply reuse the index or
results of one or more other search engines to provide
an aggregated, final set of results.
History
of popular Web search engines
The
very first tool used for searching on the Internet
was Archie. The name stands for "archive"
without the "vee". 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 file names; however, Archie did not index the contents
of these files.
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.
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
JumpStation Launch
Infoseek Launch
Lycos Launch
1995 AltaVista Launch (part of DEC)
Excite Launch
1996 Dogpile Launch
Inktomi Founded
HotBot Founded
Ask Jeeves Founded
1997 Northern Light Launch
1998 Google Launch
1999 AlltheWeb Launch
Naver Launch
Teoma Founded
Vivisimo Founded
2000 Baidu Founded
2003 Info.com Launch
2004 Yahoo! Search Final launch
A9.com Launch
2005 MSN Search Final launch
Ask.com Launch
AskMeNow Launch
Lexxe.com Founded
2006 wikiseek Founded
Quaero Founded
Ask.com Launch
Live Search Launch
ChaCha Beta Launch
Quintura Beta Launch
Guruji.com Beta Launch
2007 wikiseek Launched
AskWiki 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. JumpStation (released
in early 1994) used a crawler to find web pages for
searching, but search was limited to the title of
web pages only. One of 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) was launched, and became a major commercial
endeavor. For a more detailed history of early search
engines.
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.
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 Web search
engine.
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 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,
and ceased using results from Inktomi, now owned by
Yahoo!. In 2006, Microsoft migrated to a new search
platform - Live Search, retiring the "MSN Search"
name in the process.
Baidu
Baidu
was launched in 2000 and is the leading Chinese search
engine, providing an index of over 740 million web
pages, 80 million images, and 10 million multimedia
files. Its interface is very similar to Google's.
(Credit:
Wikipedia).
