Blackbox to blueprint: Illuminating COBOL systems

Navigating a massive COBOL codebase, crucial for many legacy systems in banking, retail, and insurance, poses a unique challenge due to decades of updates, patches, and undocumented logic. The key to understanding such systems lies in gaining observability of their core components, which can be broadly categorized into online operations, batch operations, and utilities. Tools like Swimm can assist by organizing, naming, and linking relevant files, offering visual flowcharts, and providing step-by-step code walkthroughs to clarify both screen interactions and batch operations. These tools facilitate understanding of user interactions, input validations, and batch processes, extracting and annotating critical logic to save time and effort in deciphering complex systems. Swimm's approach highlights decision logic in batch jobs, such as interest calculations, and connects input data to processing logic while also addressing edge cases and exceptions, enabling a more efficient way to modernize, debug, or modify COBOL systems.