PhD funding program with the research been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) – Research Funding Program: Heracleitus II. Investing in knowledge society through the European Social Fund, the project has focused on data mining techniques which have dealt with the scalability and qualitative content detection in recommender systems.