http://en.wikipedia.org/wiki/Search_engine

http://webopedia.internet.com/TERM/s/search_engine.html

http://www.domainsarefree.com/glossary/Search_engine.html

http://searchsoa.techtarget.com/sDefinition/0,,sid26_gci212955,00.html

http://www.answers.com/topic/search-engine

http://websearch.about.com/od/seononos/a/spamming_engine.htm

http://www.maximized.com/products/flashstats2005/beta11/docs/SearchEngines.htm

http://realestate.about.com/od/sv/g/defsearcheng.htm

http://en.wikipedia.org/wiki/Search_engine_marketing

http://www.definess.com/