EVEGA: an educational visulalization environment for graph algorithms. - Sami Khuri; Klaus Holzapfel (ITiCSE, 2001)

The complexity of detecting fixed-density clusters. - Klaus Holzapfel; Sven Kosub; Moritz G. Maaß; Hanjo Täubig (Discret. Appl. Math., 2006)

Density-based clustering in large-scale networks. - Klaus Holzapfel (2006)