1. A process of organizing program performance data in semantic groups, the performance data including multiple samples, each of the multiple samples having at least one name and at least one associated cost, the process comprising the steps of: submitting a grouping expression to a performance analysis tool, the grouping expression specifying a pattern and a replacement for grouping multiple performance data samples; and getting from the performance analysis tool a cost accounting in response to the submitting step, the cost accounting showing names of the performance data samples and associated attributed costs, all of the names being consistent with the grouping expression.