  As a software system evolves, its architecture tends to degrade, and
gradually impedes software maintenance and evolution activities and negatively
impacts the quality attributes of the system. The main root cause behind
architecture erosion phenomenon derives from violation symptoms (such as
violations of architecture pattern). Previous studies focus on detecting
violations in software systems using architecture conformance checking
approaches. However, code review comments are also rich sources that may
contain extensive discussions regarding architecture violations. In this work,
we investigated the characteristics of architecture violation symptoms in code
review comments from the developers' perspective. We employed a set of keywords
related to violation symptoms to collect 606 (out of 21,583) code review
comments from four popular OSS projects in the OpenStack and Qt communities. We
manually analyzed the collected 606 review comments to provide the categories
and linguistic patterns of violation symptoms, as well as the reactions how
developers addressed them. Our findings show that: (1) 10 categories of
violation symptoms are discussed by developers during the code review process;
(2) The frequently-used terms of expressing violation symptoms are
"inconsistent" and "violate", and the most frequently-used linguistic pattern
is Problem Discovery; (3) Refactoring and removing code are the major measures
(90%) to tackle violation symptoms, while a few violation symptoms were ignored
by developers. Our findings suggest that the investigation of violation
symptoms can help researchers better understand the characteristics of
architecture erosion and facilitate the development and maintenance activities,
and developers should explicitly manage violation symptoms, not only for
addressing the existing architecture violations but also preventing future
violations.
