In this paper we present a general method for information extraction that exploits the features of data compression techniques. We first define and focus our attention on the so-called "dictionary" of a sequence. Dictionaries are intrinsically interesting and a study of their features can be of great usefulness to investigate the properties of the sequences they have been extracted from (e.g. DNA strings). We then describe a procedure of string comparison between dictionary-created sequences (or "artificial texts") that gives very good results in several contexts. We finally present some results on self-consistent classification problems.