Extracting meaningful labels for WEBSOM text archives

Abstract

Self-Organizing Maps, being used mainly with data that are not pre-labeled, need automatic procedures for extracting keywords as labels for each of the map units. The WEBSOM methodology for building very large text archives has a very slow method for extracting such unit labels. It computes the relative frequencies of all the words of all the documents associated to each unit and then compares these to the relative frequencies of all the words of all the other units of the map. Since maps may have more than 100,000 units and the archive may contain up to 7 million documents, the existing WEBSOM method is not practical. This paper describes how the meaningful labels per map unit can be deduced by analyzing the relative weight distribution of the SOM weight vectors and by taking advantage of some characteristics of the random projection method used in dimensionality reduction. The effectiveness of this technique is demonstrated on archives of the well studied Reuters and CNN collections. Comparisons with the WEBSOM method are provided.