1. A computer-implemented method comprising: creating, by a similarity model generator of a computing device, a similarity model of a reference document stored in a database in a storage device, the similarity model of the reference document based on an adaptive entropy coding compressor; computing, by a similarity comparator of the computing device for each of the reference document and a compared document, a number of compression bits needed to compress each of the reference document and the compared document using the similarity model of the reference document; normalizing each of the computed number of compression bits for the reference document and the compared document, wherein the normalizing comprising dividing the computed number of compression bits by a number of tokens in the document being normalized; assigning each of the normalized computed number of compression bits as a similarity score for the respective reference document and the compared document; and computing, by the similarity comparator, a similarity measure between the compared document and the reference document, the similarity measure being a function of each of the similarity scores of the compared document and the reference document.
3. The computer-implemented method of claim 1 , wherein the adaptive entropy coding compressor uses a prediction by partial match model to make predictions.