Kaspar Riesen Volkmar Frinken Horst Bunke Improving Graph Classification by Isomap. 205-214 2009 GbRPR http://dx.doi.org/10.1007/978-3-642-02124-4_21 conf/gbrpr/2009 db/conf/gbrpr/gbrpr2009.html#RiesenFB09