In the literature, plenty of work has been done related to text categorization or classification in different fields. Spam e-mail detection process is handled as a 2-category (legitimate and spam e-mail) text classification problem in [Gunal et al., 2006]. Web pages are classified with a text categorization approach in [Selamat and Omatu, 2004]. The study [Shang et al., 2007] performs text categorization on a digital news database. A survey discussing the text categorization approaches from machine learning perspective is also presented in [Sebastiani, 2002].