Leveraging LLM for software modernization: COBOL Functionality Extraction Case study

Businesses are replete with applications created decades ago and are still relevant functionality wise. However, they pose significant evolution and integration challenges - the former because of paucity of skilled workforce and the latter due to high impedance mismatch with modern technology stack. The two constitute principal reasons leading to contemplation of modernization of these applications. Typical approach is to migrate existing code to the desired technology stack as a language transformation endeavor under functional equivalence. However, traditional parser-based approaches and lift-and-shift modernization methods typically add to the technology debt, thus making evolution of the modernized code even more challenging. To overcome the various lacunae in current practice in software modernization, we propose the stagewise refinement approach using LLM. In this paper, we focus on the stage of human-in-theloop automation aided generation of functionality description specifically for Common Business-Oriented Language (COBOL) code. We illustrate the utility and efficacy of the proposed approach through validation on a small but complex business application.