Frank M. Shipman III Hao-wei Hsieh Preetam Maloor J. Michael Moore The visual knowledge builder: a second generation spatial hypertext. 113-122 2001 conf/ht/2001 Hypertext http://doi.acm.org/10.1145/504216.504245 db/conf/ht/ht2001.html#ShipmanHMM01