Search Engines

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Links to Search Engines

What is a search engine and how does it work?

The Big Three

There are three major "spiders" Tehoma (Ask), Google and Yahoo. With the exception of MSN Live Search, every search engine uses a variation of one of the three major spiders.



Meta-search Engines	Smaller Search Engines & Directories	Specialized Search Engines
Search multiple search engines all at once.	Directories are links to webpages set up by a person.	Useful for specific subjects.


Groups search terms into subject clusters.	A simplified Yahoo search.	A comparison shopping search.


Searches Google, Yahoo, Ask, MSN Live, and more.	Microsoft's entry into search engines.	Looks for scientific information


Easy Access to the web's three major crawler based search engines: Yahoo, Google and Ask.	A directory of web pages by subject. Also has a blog directory.	A Travel search engine


Can mix search with educational, US Govt and news sources.	A directory set up by a Consortium of library schools	Family friendly image search.

What is a search engine and how does it work?

Search engines do not really search the World Wide Web directly. Each one searches a database of web pages that it has found. The search engines use software programs (often referred to as "spiders", "webcrawlers", or "robots") to collect information, which is then indexed by the search engine.

These "spiders" crawl the web, finding pages for potential inclusion by following the links in the pages they already have in their database. The search engine spider can not find a web page unless the web page is linked from another page. This means the web pages with the most links from other web pages are listed first, so less popular but useful web pages can get lost in the numbers. New pages can get into a search engine only if other pages to link to it, or if a human to submits its address (URL) to the search engine for inclusion.

Many web pages are excluded from most search engines. Databases such as article databases and library catalogs, are excluded because search engine spiders cannot access them. All this material is referred to as the "Invisible Web" because you don't see in search engine results.