Learning GENERAL Principles from Hundreds of Software Projects

When one exemplar project, which we call the "bellwether", offers the best advice then it can be used to offer advice for many other projects. Such bellwethers can be used to make quality predictions about new projects, even before there is much experience with those new projects. But existing methods for bellwether transfer are very slow. When applied to the 697 projects studied here, they took 60 days of CPU to find and certify the bellwethers. Hence, we propose a GENERAL: a novel bellwether detection algorithm based on hierarchical clustering. At each level within a tree of clusters, one bellwether is computed from sibling projects, then promoted up the tree. This hierarchical method is a scalable approach to learning effective models from very large data sets. For example, for nearly 700 projects, the defect prediction models generated from GENERAL's bellwether were just as good as those found via standard methods.