The loss of architectural knowledge during system evolution: An industrial case study

Architecture defines the components of a system and their dependencies. The knowledge about how the archi-tecture is intended to be implemented is essential to keep the system structure coherent and thereby comprehensible. In practice, this architectural knowledge is explicitly for-mulated only in the documentation (if at all), which usually gets outdated very soon. This leads to a growing amount of implicit knowledge during evolution that is especially volatile in projects with high developer fluctuation. In this paper we present a case study about the loss of architectural knowledge in three industrial projects to an-swer the following research questions: 1) to what degree is the architectural documentation kept in conformance with the code? 2) how well does the documentation reflect the in-tended architecture?, 3) how big is the architectural decay?, and 4) what are the causes for nonconformances? We an-swer these questions by investigating the architecture doc-umentation, the source code, and by performing interviews with developers. The most important outcomes of our study are: the in-formal documentation and the source code are not kept in conformance with each other, none of them completely re-flects the intended architecture, and even developers taken individually are not completely aware of the intended ar-chitecture. Quantitatively, between 70 % and 90 % of these nonconformances are caused by flaws in the documentation and between 10 % and 30 % represent architectural viola-tions in the code.