1. In a computing system for identifying populations of events in a multi-dimensional data set obtained from a flow cytometer, the populations associated with blood components in a sample of human or animal blood, the improvement comprising: one or more machine readable storage media for use with the computing system, the machine readable storage media storing: a) data representing a finite mixture model, the model comprising a weighted sum of multi-dimensional Gaussian probability density functions associated with populations of events expected in the data set; b) an expert knowledge set comprising (1) one or more data transformations and (2) one or more logical statements, the transformations and logical statements encoding a priori expectations as to the populations of events in the data set; and c) program code for the computing system comprising instructions for operating on the multi-dimensional data using the finite mixture model and the expert knowledge set to thereby identify populations of events in the multi-dimensional data set associated with said blood components.