Let's now start to examine what are the different aspects and phases in the design of an IV system. First, there is a selection issue. We have a large number of data available, a large dataset, but we have to ask ourselves which of this data are useful to the currently considered task. For example, if we have a dataset with fiscal data of a number of citizens, with 20 or 30 different variables for each citizen, but we are just interested in seeing who is the richest man in the country maybe it is sufficient to select one variable among all the variables we have recorded in our dataset.