1. A computer-implemented method for processing data, comprising: receiving an input from a user comprising positive examples and negative examples of a specified data type, the positive examples comprising first character strings that belong to the specified data type, and the negative examples comprising second character strings that do not belong to the specified data type; processing the first and second character strings to create a set of attributes that characterize the positive examples; building a decision tree, based on the attributes, which when applied to the first and second strings, distinguishes the positive examples from the negative examples; and applying the decision tree to the data so as to identify occurrences of the specified data type.