“…First, design patterns are commonly used in both open-source and proprietary software and are seen as an exemplar of sound software engineering practice; knowledge of their change trends and fault-proneness is valuable information for the developer and could also inform future maintenance activity, resource prioritization, and QA planning. While we agree that in theory use of design patterns should be condoned, we see the study presented as an exploration of actual design pattern usage and evolution in an industrial setting (Kemerer & Slaughter, 1999); the purpose of any empirical software study is to support (or refute) hypoth-eses (possibly using metrics) about the way we develop and use software in all its aspects (Basili, Briand, & Melo, 1996;Chidamber & Kemerer, 1994). Second, detailed studies of fault data in large scale commercial software systems are rare and this study reports, not only on fault occurrence, but also documents corrective maintenance measurements, in terms of lines of code, which may add valuable information for the prediction of future maintenance effort.…”