What is Search Engine and Its Working

A software program or script available through the Internet that searches documents and files for keywords and returns the results of any files containing those keywords.A search engine is really a general class of programs, however, the term is often used to specifically describe systems like Google, Bing and Yahoo! Search that enable users to search for documents on the World Wide Web.

 Today, there are thousands of different search engines available on the Internet, each with their own abilities and features. Today, the most popular and well known search engine is Google.

Web search engines work by sending out a spider to fetch as many documents as possible. Another program, called an indexer, then reads these documents and creates an index based on the words contained in each document. Each search engine uses a proprietary algorithm to create its indices such that, ideally, only meaningful results are returned for each query.

·         A spider (also called a "crawler" or a "bot") that goes to every page or representative pages on every Web site that wants to be searchable and reads it, using hypertext links on each page to discover and read a site's other pages

·   A program that creates a huge indexer (sometimes called a indexer or "catalog") from the pages that have been read.

·   A program that receives your search request, compares it to the entries in the index, and returns results to you.

·   Major search engines such as Google, Yahoo (which uses Google), AltaVista, and Lycos index the content of a large portion of the Web and provide results that can run for pages - and consequently overwhelm the user.

 Working :-

In the picture to the right, is an example of how a search engine works. As can be seen in the image, the starting point of all search engines is a spider or crawler, which visits the pages that will be included in the search and grabs the contents of each of those pages.

Once a page has been crawled the data contained within the page is processed, often this involves stripping out stop words, grabbing the location of each of the words in the page, the frequency they occur, links to other pages, images, etc. This data is used to rank the page and is the primary method a search engine uses to determine if a page should be shown and in what order.

Finally, once the data has been processed it is often broken up into one or more files, moved to different computers or servers, or loaded into memory where it can be accessed when users perform a search.

Different types of the major search engines:-

Search Engines	Types
Google	Crawler-based search engine
AllTheWeb	Crawler-based search engine
Teoma	Crawler-based search engine
Inktomi	Crawler-based search engine
AltaVista	Crawler-based search engine
LookSmart	Human-Powered Directory
Open Directory	Human-Powered Directory
Yahoo	Human-Powered Directory, also provide crawler-based search results powered byGoogle
MSN Search	Human-Powered Directory powered byLookSmart, also provide crawler-based search results powered by Inktomi
AOL Search	Provide crawler-based search results powered by Google
AskJeeves	Provide crawler-based search results powered by Teoma
HotBot	Provide crawler-based search results powered by AllTheWeb, Google, Inktomiand Teoma, “4-in-1” search engine
Lycos	Provide crawler-based search results powered by AllTheWeb
Netscape Search	Provide crawler-based search results powered by Google

Table 1: Different types of the major search engines

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