M. Jonsson. Proceedings of the 2007 International Conference on Mobile Data Management, page 304--308. Washington, DC, USA, IEEE Computer Society, (2007)
P. Heymann, A. Paepcke, and H. Garcia-Molina. Third ACM International Conference on Web Search and Data Mining (WSDM2010), page 1--10. Stanford University, (February 2010)