Design maintenance: unexpected architectural interactions (experience report)

There have been many systems developed that attempt to recover design and structure from code. We present our experience with using one such tool, SoFi, to extract design structure from a large industrial system written in C. We compare the extracted structure to that which was intended by the designers of the system. We observe and categorize, for our system, the reasons why these two views differ. We observe that seemingly minor decisions in implementation, can have a large impact an the extracted design, and draw some conclusions about the practicality of trying to recover "intended designs" from source code.