How well can we predict changes at architecture design time ? q 3

9 Two years ago, we analyzed the architecture of Sagitta 2000/SD, a large business information system being developed on behalf 10 of Dutch Customs. We were in particular interested in assessing the capabilities of the system to accommodate future complex 11 changes. We asked stakeholders to bring forward possible changes to the system, and next investigated how these changes would 12 affect the software architecture. Since then, the system has been implemented and used, and actual modifications have been proposed 13 and realized. We studied all 117 change requests submitted since our initial analysis. The present paper addresses how well we have 14 been able to predict complex changes during our initial analysis, and how and to what extent the process to elicit and assess the 15 impact of such changes might be improved. This study suggests that architecture analysis can be improved if we explicitly challenge 16 the initial requirements. The study also hints at some fundamental limitations of this type of analysis: (1) fundamental modifiability17 related decisions need not be visible in the documentation available, (2) the actual evolution of a system remains, to a large extent, 18 unpredictable and (3) some changes concern complex components, and this complexity might not be known at the architecture level, 19 and/or be unavoidable. 2