> Imagine dealing with say COBOL where even the team who was hired to maintain it is going to retire. It's the closest to "lost technology" trope from Sci-Fi we

> Imagine dealing with say COBOL where even the team who was hired to maintain it is going to retire. It's the closest to "lost technology" trope from Sci-Fi we have ever been. The technical aspect of the code is not actually the difficult part WRT maintenance. Someone that knows COBOL as a language can figure out what some code does and how it does it. It takes time but that is information that can be derived if you just have the code. The main problem with COBOL is the code is often an implementation of some business or regulatory process. The COBOL maintainer retiring is taking knowledge of the code but more importantly the knowledge of the literal business logic. The business logic and accounting/legal restraints aren't something that can necessarily be derived from the code. You can know some bit of code multiplies a value to 100 but you can't necessarily know if it supposed to do that. If the source code and documentation don't capture the why of the code the how doesn't help the future maintainer. Often with COBOL the people that originally defined the why of the code are not just retired but dead. The first generation of maintainers may only have ever received partial knowledge of the why so even the best documenters have holes in their knowledge. They may have had exposure to the original why defines but neglected or didn't have an opportunity to document some aspects of why. The subsequent generations of maintainers are constrained by how much of the original why was documented. Edit: pre-coffee typo