Guido Zuccon Leif Azzopardi C. J. van Rijsbergen Semantic Spaces: Measuring the Distance between Different Subspaces. 225-236 2009 QI http://dx.doi.org/10.1007/978-3-642-00834-4_19 conf/qi/2009 db/conf/qi/qi2009.html#ZucconAR09