title: data bubbles for non-vector data : speeding-up hierarchical clustering in arbitrary metric spaces. authors: jörg sander , jianjun zhou. venue: vldb. year: 2003
title: data bubbles : quality preserving performance boosting for hierarchical clustering. authors: markus m. breunig , hans-peter kriegel , peer kr &#246; ger , j &#246; rg sander. venue: international conference on management of data. year: 2001