1. B. Babcock, M. Datar, R. Motwani, and L. O'Callaghan, "Maintaining Variance and k-Nedians Over Data Stream Windows," 2003 PODS. See PS, PDF, etc..

2. Other references (including links to on-line sources) are in Old Bibliography. See the papers:
   • P. Bradley, U. Fayyad, and C. Reina, ``Scaling Clustering Algorithms to Large Databases,'' 1998 KDD.
   • S. Guha, R. Rastogi, and K. Shim, ``CURE: An Efficient Clustering Algorithm for Large Databases,'' SIGMOD 1998.