Mattias Andersson Joachim Gudmundsson Christos Levcopoulos Approximate Distance Oracles for Graphs with Dense Clusters. 53-64 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3341&spage=53 2004 conf/isaac/2004 ISAAC db/conf/isaac/isaac2004.html#AnderssonGL04