1. A method performed on a computer system for estimating a cardinality value for a set of data values, comprising the steps of: (a) initializing a data structure for representing counts; (b) obtaining a data value from said set of data values; (c) transforming said data value into a transformed string; (d) modifying said data structure with said transformed string; (e) obtaining a summary statistic value from said modified data structure; and (f) generating said estimated cardinality value using said summary statistic value.