Have you heard of Swoogle?
You can find this search engine at http://swoogle.umbc.edu/index.php?option=com_frontpage&service=search&queryType=search_swt&searchStart=1&searchString=
Swoogle is a search engine for Semantic Web Ontologies, documents, terms and data found on the web. Swoogle provides services to human users through a browser interface and to software agents via RESTful web services. Swoogle employs Resource Description Framework (RDF) semantic technique - and other semantic technique is Topic Map which you may aware of that.
Swoogle is a research project (PhD thesis work of Li Ding) developed at and is hosted by the University of Maryland, Baltimore County. This project received funding from US DARPA and NSF.
You can read more at - http://www.searchenginejournal.com/swoogle-an-engine-for-the-semantic-web/5469/