1. A computer-implemented method for determining a window size for outlier detection in a time series of a database system managed by a processor, said method comprising: calculating strength values for data points with said processor using a plurality of window sizes, resulting at least in a plurality of strength values for each window size, said strength values increasing as a distance between a value of a respective data point and a local mean value increases; calculating, for each said plurality of strength values associated with a said window size, a weighted sum based on the respective plurality of strength values with said processor using a weighting function suppressing effect of largest strength values, and selecting a window size with said processor based on said weighted sum.