Suppose you want to analyze the performance of a function whose attributes of the input data are variable. Thus, different sets of data can be passed as parameters of this function, and each data set corresponds to a specific instance. In fact the performance of the function can be analyzed based on run time and / or memory consumption, and caracteristics as input data size are important to determine actual function performance. To choose characteristics instances means choosing data sets that represent of complete way of occurrences to assess such performance.