A method for calculating term similarity on large document collections

We present an efficient algorithm called the Quadtree Heuristic for identifying a list of similar terms for each unique term in a large document collection. Term similarity is defined using the expected mutual information measure (EMIM). Since our aim for defining the similarity lists is to improve information retrieval (IR), we present the outcome of an experiment comparing the performance of an IR engine designed to use the similarity lists. Two methods were used to generate similarity lists: a brute-force technique and the Quadtree Heuristic. The performance of the list generated by the Quadtree Heuristic was commensurate with the brute force list.