At present, some of the main search engines provide search services are:
1) combined with keyword search directory (Browsing & Searching Integration)
this type of search tool is Sohu (http://s.www.sohu.com).
2) (Precise Search) accurate retrieval
the accurate search in two ways, one is the use of controlled vocabularies, another is the use of XML technology.
3) natural language retrieval (Natural Language Search)
4) (Multilingual) multilingual retrieval;
5) multimedia retrieval (Multimedia Search)
6) (Filtered Search) filter retrieval <.