1. A method of comparing spans of text comprising: computing a similarity measure between a first sequence of symbols representing a first text span and a second sequence of symbols representing a second text span as a function of the occurrences of optionally noncontiguous subsequences of symbols shared by the two sequences of symbols, wherein each of the symbols comprises at least one consecutive word, the words being enriched with linguistic information allowing them to be defined according to a set of linguistic factors, whereby pairs of symbols in the first and second sequences forming a shared subsequence of symbols are each matched according to at least one of the factors and wherein all pairs of matching symbols in a shared subsequence need not match according to the same factor.