When a software system evolves, features are added, removed and changed. Moreover, refactoring activities are periodically performed to improve the software internal structure. A class may be replaced by another, two classes can be merged, or a class may be split in two others. As a consequence, it may not be possible to trace software features between a release and another. When studying software evolution, we should be able to trace a class lifetime even when it disappears because it is replaced by a similar one, split or merged. Such a capability is also essential to perform impact analysis. This paper proposes an automatic approach, inspired on vector space information retrieval, to identify class evolution discontinuities and, therefore, cases of possible refactoring. The approach has been applied to identify refactorings performed over 40 releases of a Java open source domain name server. Almost all the refactorings found were actually performed in the analyzed system, thus indicating the helpfulness of the approach and of the developed tool.