1c. Types of Search Engines
 

·         Crawler-based Search Engines – such as Google, Yahoo & Live, use software (also called robot, crawler, or spider) to automatically add new pages in their databases (index). It has three major elements:

o        Spider or crawler – visits a web page, reads it and then follow links to other sites.

o        The Index - everything the spider finds goes into the index like a giant book containing a copy of every page that the spider finds.

o        Search Engine software – a program that search through the millions of pages recorded in the index to find matches to a search and rank them of what it believes is most relevant. 

·         Human-powered Directories – such as Yahoo Directory, Open Directory Project (DMOZ) etc., use human to manually fill and manage their databases.

·         Meta Search Engines – like MetaCrawler.com, DogPile.com etc. combines results from a number of search engines and display them at the same time.

·         Pay-per-Performance & Paid Inclusion Engines - that accepts fee to keep your site listed, re-spidered, or top-ranked for keywords of your choice.  

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