  Mainframe systems are facing a critical shortage of developer workforce as
the current generation of COBOL developers retires. Furthermore, due to the
limited availability of public COBOL resources, entry-level developers, who
assume the mantle of legacy COBOL systems maintainers, face significant
difficulties during routine maintenance tasks, such as code comprehension and
defect location. While we made substantial advances in the field of software
maintenance for modern programming languages yearly, mainframe maintenance has
received limited attention. With this study, we aim to direct the attention of
researchers and practitioners towards investigating and addressing challenges
associated with mainframe development. Specifically, we explore the scope of
defects affecting COBOL systems and defect location strategies commonly
followed by COBOL developers and compare them with the modern programming
language counterparts. To this end, we surveyed 30 COBOL and 74 modern
Programming Language (PL) developers to understand the differences in defects
and defect location strategies employed by the two groups. Our preliminary
results show that: (1) major defect categories affecting the COBOL ecosystem
are different than defects encountered in modern PL software projects; (2) the
most challenging defect types in COBOL are also the ones that occur most
frequently; and (3) COBOL and modern PL developers follow similar strategies to
locate defective code.
