Fig. 11

Process of string transformation. The process of string transformation implies conversion and filtering of a string. Initially, the string is converted to lower case. Then it passes through regular expression filtering to extract alphabetic and numeric characters [a-z, 0–9]. The string is then purified by eliminating words that are in the list of stop words. This list contains high-frequency words with relatively low information content (function words and pronouns). Finally, suffix removal is performed by applying Porter‘s Stemming Algorithm [52]