1. Perlis, A.J.: Sayward, F.G., Shaw, M., (MIT Press 1981),Software metrics,
2. Conte, S.D., Shen, V.Y., and Dunsmore, H.E.: (Benjamin Cummins Publishing Inc. 1986),Software engineering metrics and models,
3. Jones, C.B.: (Prentice Hall 1986),Systematic software development using VDM,
4. Morgan, C.: (Oxford University PRG 1984),Schemas in Z — a preliminary reference manual,