1. A Conceptual Framework, M. E. Bush and N. E. Fenton,Software Measurement Journal of Systems and Software, vol. 12 pp 223–231, 1990.
2. N. R. Campbell, Cambridge University Press, 1920 Physics, The Elements,(reprinted as Foundations of Science, Dover, 1957 ).
3. Theory and Philosophy of Measurement, L. Finkelstein, in Handbook of Measurement Science, Volume 1: Theoretical Fundamentals, P. H. Sydenham (ed.), Wiley, 1982.
4. N. E. Fenton, Chapman and Hall, 1991.Software Metrics:A Rigorous Approach
5. F. J. Heemstra and R. Kusters, University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands, Controlling Software Development CostsA Field Study, 1988.