Impact analysis is the identification of the work products affected by a proposed change request, either a bug fix or a new feature request. In many open-source projects, such as KDE, Gnome, Mozilla, Openoffice, change requests, and related data, are stored in a bug tracking system such as Bugzilla [1]. These data, together with the data stored in a versioning system, such as CVS [2], are a valuable source of information on which useful analyses can be performed.

In this paper we propose a method to derive the set of source files impacted by a proposed change request. The method exploits information retrieval algorithms to link the change request description and the set of historical source file revisions impacted by similar past change requests. The method is evaluated by applying it on four open-source projects.