Classifications of search engines

New types of search engines are emerging to overcome the defects of traditional search engines and improve the efficiency of search. So many types of search engines are reported, such as faceted search, ontology-based search, concept-based search, rule-based search, and so on.
Search engines can be classified into:
*Primary search engines
-Google
-Yahoo
-MSN
This category of search engines can be characterized as those which collect the information from WWW on their own and organize, store and manage their indices. Since, these engines compile and manage own databases, they require larger storage capacity and computing power.

*Secondary search engines
A secondary search engines process the results of a primary search engine. Resource consumption is much less because of using the already existing index of the primary search engine (e.g. bandwidth, disk storage and computational power to build an index are not needed).

*Targeted search engines
Sometimes called topical search engines - are the most specific of them all. These search engines are very narrowly focused, usually to a general topic, such as medicine or branches of science, travel, sports and so on.
Classifications of search engines