Available approaches for keyword based querying RDF federations

Hi,

I would like to know available approaches for  keyword based querying RDF
federations.

I found the following approach :
FedSearch: Efficiently Combining Structured Queries and Full-Text Search in
a SPARQL Federation by
Andriy Nikolov
<http://link.springer.com/search?facet-author=%22Andriy+Nikolov%22>,
Andreas Schwarte
<http://link.springer.com/search?facet-author=%22Andreas+Schwarte%22>,
Christian Hütter
<http://link.springer.com/search?facet-author=%22Christian+H%C3%BCtter%22>

I would like to know whether there are any other approaches.

Regards,
Thilini Cooray