Boehm, Barry, et al. Software Cost Estimation with Cocomo II. Reading, MA: Addison-Wesley, 2000. Boehm provides a brief description of Object Points.
Lorenz, Mark and Jeff Kidd. Object-Oriented Software Metrics. Upper Saddle River, NJ: PTR Prentice Hall, 1994. Lorenz and Kidd present numerous suggestions of quantities that can be counted in object-oriented programs.