1. International Standard‘Information technology: software product evaluation–quality characteristics and guidelines for the their us’, ISO 9126-1, 2000 International Organization for Standardization, Geneva
2. Chung, L., Nixon, B., Yu, E., and Mylopoulos, J.: ‘Non-functional requirements in software engineering’, (Kluwer Academic Publishers 2000)
3. International Standard‘Information technology: software product evaluation–external and internal metrics’, ISO 9126-2,3, 2003 International Organization for Standardization, Geneva
4. Klein, M., Ralya, T., Pollak, B., Obenza, R., and Gonzlez Harbour, M.: ‘A practitioner's handbook for real-time systems analysis’, (Kluwer Academic Pub 1993)