Search Engines are interactive web sites which are help to find your interested web sites from Internet. Every Search engines have their own rules & ways for search sites. Lot of search engines handle own giant database related to all  websites in internet. Normally search engine have text box which you can simply enter your search topic, then after you press search button, then they give results of web sites which include title, short description & URL. Yahoo! was first web index or directory were lunched by David Filo & Jerry Yang in 1994 August. AltaVista was lunched by Digital Equipment Corp, was first search engine (1995 December), While Google is most popular search engine which was started in 1999 September. More than them, there have huge number of search engines for search internet contents, focusing eyes on new websites & grabbing websites from internet to their giant databases.
 
 Example Search engine results :

What are spiders or crawlers ?
Main tool of any search engine is, spiders or crawler (or robots or worms or trawlers) which is software program, or can called as text only self surf web browser, which can go into one site then follow it's links and index about that site in their database. Search engine use Submit Your Site link to know about new sites. So if one site have links to other web site, then spider go into that site also. Normally spider visit all sites which include their database once a month to verify that site is updated or changed. After spidered or crawled, search engine take copy of every page which was spidered. it is called indexed. But to indexed it will take one week to six months. Therefore site which is spidered will not indexed in their database. Some search engines hire database such as InkTomi for there searching while other do combine search with other search engines for results (as Dogpile). But all search engine's search results are not same cause they have their own search logic. Check Yahoo! & AltaVista, even they are now belongs to same company.

How search engines categorize & rank web sites :

1. According to subject category - As example : Space » Astronomy » stars » pulsers » etc...
2. Spidered copy - use every words of every web pages in site 
3. According to meta tags : Title, Description, Category & Keywords 
4. Ranking site with visitors hitting in search results 
5. Number of links to outer sites in particular site 
6. Number of links from other sites to particular site
7. Updating speed or submitted date 
8. Web personality, HTML tags or technical features of web sites 
9. According to particular order such as as A toZ  or 1 to 10... 
10. According to domain names (also called es URL), sub domain names or words in domain names
11. By runing server side programs such as PHP, JSP, ASP, etc... - http://www.site.com/page.php?friends
12. Amount of multimedia contents such as videos, images, flash, audio types, etc...

  Search engine types :

1. Spider Searchers - use spider for copy whole web site into their databases (as Google)
2. Web Guiders - web site organize by subject wise sections (as Yahoo!)
3. Meta Searchers - use site's meta tags for index in other search engine's databases (as Dogpile)
4. Subject Wise - crawel the web according to particular subject or only one topic (as Medscape)
5. Media Searchers - crawel the web for search images, songs, videos, etc... (as ImageLanka)
6. Search Portals - give search results with other portal services such as emails or news (as Exicte)
7. Gateways - handle links to other web sites without particular topic (as Dmoz)
8. Rings - use circle linking system among sites of same category or subjects (as webcam WebRing)
9. Directories - handle links with particular country or subjects (as E-Sangha on Buddhism)
10. Yellow Pages - categorize business's emails, addresses and company details
11. White Pages - categorize people's emails, addresses and personal details (as WhoWhere)
12. Friends Finders - find people for relationships such as love, sex, penpals, etc... (as FaceBook) 

  Which Search Engine Is Good When?

• Need information has been published in past years back - Try HotBot
• Need check particular URL is available - Use Google
• Want to find lot of information in certain topic in same web page - Use Alta Vista with NEAR keyword
• Want to find web page witch no longer exit - Try in Google cache
• Need to find certain event that goes with time line - Use Vivisimo
• Help to school children for find information with school project - Use Yahoo!
• Remember Yahoo! is like library, so if you want search about educational topic - Use Yahoo!
• Quick finding about particular subject which is not certain - Use Dmoz
• If you need to know about certain things, place or topic - Use Google
• Top 10 sites in particular topic - Use DogPile like meta search engines

Doing advanced searching

• Quotes ('') - words must be include in order in search results. Ex : 'lanka' 'economic' 'stock' will give results about stock information in economic web sites in Sri Lanka.
• Plus (+) or AND - words must be include without order in search results. Ex : astrology +Indian +China will give results sites have details about Astrology about India and China.
• Minus (-) or NOT - words must not include in search results. Ex : culture -music -dance will give results cultural web pages which are not include music and dance.
• OR - search multiple words in different topics. Ex : penpal OR love OR history will give results all pages have words penpal, love and histroy.
• NEAR - search terms with near relationship between two words,  in same sentence, or paragraph in same document. Ex.. government NEAR policy will search policy of the government
• ADJ - use to search about topic. Here first word is main topic and sub words about main topic.  Ex.. china ADJ government will search document about china.
• SAME / WITH used to search words in same sentence or paragraph.
• Asterisk (*) - words begin & end with some multiple characters. Ex : com* will give topic related to computer, company, commnucation. You must need four begin characters.
• Percent (%) - words begin & end between one character hidden. Ex : ga%l will give topic related to gaol, gael, gall,etc. Some search engines there have no different between * and %.
• Except Quote other search literals can't use with one word. Ex : Wrong +dog, -cat, OR culture
• You can use mixing these search literals. Ex : Lanka +music -dance OR India
• Always try to construct your own search phrases with combining in advance search keywords.
• Always read FAQ, Search Tips, Advance Search - pages in any search engines