Desislava Petkova W. Bruce Croft Yanlei Diao Refining Keyword Queries for XML Retrieval by Combining Content and Structure. 662-669 2009 ECIR http://dx.doi.org/10.1007/978-3-642-00958-7_63 conf/ecir/2009 db/conf/ecir/ecir2009.html#PetkovaCD09