Bug reports are artifacts that track the defects of software systems. In software maintenance research area, there has been a bunch of research work addressing problem of bug reports in recent years.
Bugzilla is one of the most popular bug reporting system. For the sake of its popularity and open-source feature, the data for research are largely provided by Bugzilla.
The diagram below shows the major categories of work in this area. The left-bottom corner is a sample bug report from Bugzilla.