An Empirical Study of Architectural Change in Open-Source Software Systems

From its very inception, the study of software
architecture has recognized architectural decay as a regularly
occurring phenomenon in long-lived systems. Architectural decay
is caused by repeated changes to a system during its lifespan.
Despite decay’s prevalence, there is a relative dearth of empirical
data regarding the nature of architectural changes that may lead
to decay, and of developers’ understanding of those changes. In
this paper, we take a step toward addressing that scarcity by
conducting an empirical study of changes found in software
architectures spanning several hundred versions of 14 opensource
systems. Our study reveals several new findings regarding
the frequency of architectural changes in software systems, the
common points of departure in a system’s architecture during
maintenance and evolution, the difference between system-level
and component-level architectural change, and the suitability
of a system’s implementation-level structure as a proxy for its
architecture.