Find Information and Resources online
Search Engines
Search engine
From Wikipedia, the free encyclopedia.
The phenomenal success of the Google search engine was mainly
due to its powerful Pagerank algorithm and its
simple, easy-to-use interface.
A search engine is a program designed to
help find files stored on a computer, for example a public
server on the World Wide Web, or one's
own computer. The search engine allows one to ask for media content meeting
specific criteria (typically those containing a given word or phrase) and retrieving a list of
files that match those criteria. A search engine often uses a previously made,
and regularly updated index to look for files after the user has entered search
criteria.
|
|
In the context of the Internet, search engines usually refer to the World
Wide Web and not other protocols or areas. Furthermore search engines mine data
available in newsgroups, large databases, or open directories like DMOZ.org.
Because the data
collection is automated, they are distinguished from Web
directories, which are maintained by people.
The vast majority of search engine are run by private companies using
proprietary algorithms and closed databases, the most popular currently being Google (with MSN
Search and Yahoo! closely behind). There
have been several attempts to create open-source search engines,
among which are Htdig, Nutch, Egothor and OpenFTS. [1] (http://www.searchtools.com/tools/tools-opensource.html)
How search engines work
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 — an automated web browser which follows every link it sees. 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.
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.
There is another main type:Real-time search engines, like Orase (http://www.orase.com). Such search engines
don't use an index. The information that a search engine needs is only collected
if a new query is started. Compared to the index based systems of Google-like
search engines this real-time system has some advantages:The information are
always up-to-date, there are (almost) no dead links and less system resources
are needed. (Google uses almost 100.000 computers, Orase only one.) But there
are some disadvantages, too:A search needs longer to be finished, for
example.
The usefulness
of a search engine depends on the relevance of the results 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.
History
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. One of the first engines to later become a major commercial
endeavor was Lycos,
which started at Carnegie Mellon
University as a research project in 1994.
Soon after, many search engines appeared and vied for popularity. These included WebCrawler,
Hotbot, Excite, Infoseek, Inktomi, 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.
In 2002, Yahoo! acquired Inktomi and in 2003, Yahoo!
acquired Overture, which owned AlltheWeb and Altavista. 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.
In December 2003, Orase
published the first version of its new real-time search technology. It came with
many new functions and the performance increase a lot.
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
offerings. Some have completely taken off their public search engine, and
are marketing Enterprise-only editions, such as Northern Light (http://www.northernlight.com/) which use to be
part of the 8 or 9 early search engines after Lycos came out.
Before the advent of the Web, there were search engines for other protocols or
uses, such as the Archie search
engine for anonymous FTP sites and
the Veronica search
engine for the Gopher protocol.
Osmar R. Zaďane's From
Resource Discovery to Knowledge Discovery on the Internet details the
history of search
engine technology prior to the emergence of Google.
Recent additions to the list of search engines include a9.com, AlltheWeb, Ask
Jeeves, Clusty, Gigablast, Ez2Find, Teoma, WiseNut, GoHook, Kartoo,
and Vivisimo.
Google
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.
Researchers at NEC Research
Institute claim to have improved upon Google's patented PageRank technology by
using web crawlers to find "communities" of websites.
Instead of ranking pages, this technology uses an algorithm that
follows links on a webpage to find other pages that link back to the first one
and so on from page to page. The algorithm "remembers" where it has been and
indexes the number of cross-links and relates these
into groupings. In this way virtual communities
of webpages are found.
Challenges faced by search engines
- The web is growing much faster than any present-technology search engine
can possibly index (see distributed web
crawling).
- Many web pages 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 results in many false positives.
- Dynamically generated sites, which may be slow or difficult to index, or
may result in excessive results from a single site.
- Many dynamically generated sites are not indexable by search engines; this
phenomenon is known as the invisible web.
- Some search engines do not order the results by relevance, but rather
according to how much money the sites have paid them.
- Some sites use tricks to manipulate the search engine to display them as
the first result returned for some keywords. This can lead to some search
results being polluted, with more relevant links being pushed down in the
result list.
See also
External links
|
