1. A computer implemented method of querying a database comprising: (a) receiving one or more target sequences of digital data into a computer memory, wherein each sequence of digital data (SDD) comprises subsequences; (b) computing a numerical similarity signature, referred to as an equivalence signature, for a target SDD; (c) computing a fundamental homotopy group's invariant of a subsequence as the difference between the last and first values of said subsequences, wherein homotopy invariants characterize equivalence classes of maps between topological spaces; (d) reducing the equivalence signature to a sum over the number of subsequences that constitute said target SDD with each summand being positive one (+1) if the value of a fundamental homotopy group's invariant for the values of the elements of a subsequence is even, and negative one (−1) if said value of the fundamental homotopy group's invariant for said values of the elements of said subsequence is odd; (e) creating a first set of one or more similar sequences of digital data by computing a similarity distance between the computed target equivalence signature and candidate equivalence signatures that were previously stored in a database; wherein in order for a candidate SDD to be identified as being similar to a target SDD, the absolute value of the difference of their equivalence signatures will either be equal to each other or differ by a predetermined bounded value that is less than the lesser of the two numbers of subsequences in said sequences of digital data; and (f) performing further analysis on said first set of one or more similar sequences, using secondary features and meta data, in order to produce a final set of one or more similar sequences.