Empirical observations on object evolution

A class evolves to address new user requirements and enhance reusability. The evolution processes can be analyzed statistically by tracing quantitative characteristics of object-oriented software development cases. In our case studies, increasing phenomena have been observed by four layers: a system layer, a class tree layer, a class layer and a method layer. Quantitative data, the value of mean lines of code per method over classes belonging to the same inheritance tree, can be considered to represent a characteristic of the inheritance tree over evolution and to affect class evolution as a constraint. Another type of data, the distribution pattern of size data at the system layer, is fitted to the negative binomial distribution model, and the parameters of the model can be interpreted to disclose some development intentions. This paper reports the results of empirical case studies and discusses evolution patterns and laws of objects.