Measuring Legacy Software Systems: A Goal–Question–Metric (GQM)-Based Framework

Legacy software systems continue to support critical organizational operations, yet organizations often lack a structured and quantitative way to assess their actual condition. This paper presents a multidimensional framework based on the Goal–Question–Metric (GQM) paradigm for measuring legacy software systems in organizational technical environments. The framework was developed through GQM sessions, workshops, and discussions with technical leaders and specialists, with an emphasis on objective and quantifiable metrics. It covers seven measurement directions: breadth, depth, risk of slippage toward legacy software systems, software aging coefficient, human technical capability immersion, seasonality, and substitutability. Breadth is further examined through general existence, individual existence, quality, and user functionality. The proposed measures are expressed through interpretable numerical formulations and combined into an overall Legacy Software System Measurement Model for individual software systems. The framework was applied to thirteen software systems across five organizational cases representing public, private, semi-government, and international contexts. The results show that the proposed measures can distinguish acceptable, pre-risk, and risk conditions and reveal differences among systems that may not be identified through software age alone. The framework therefore provides a structured basis for comparing legacy software systems and supporting evidence-based decisions concerning maintenance, modernization, reengineering, and replacement.