@inproceedings   {Zhang_Guan:Variance_PODS2007,
    author       = "Linfeng Zhang and Yong Guan",
    title        = "Variance Estimation over Sliding Windows",
    booktitle    = "Proceedings of the 26th ACM SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems (PODS 2007)",
    address      = "Beijing, China",
    month        =  Jun,
    year         = "2007"
};