The train schedule as seen by passengers stays the same for years, often to the rail number in stations. What changes are the crews, wagons, locomotives, possib

The train schedule as seen by passengers stays the same for years, often to the rail number in stations. What changes are the crews, wagons, locomotives, possibly routes on the railway (switches and reactions to delays and failures.) A friend of mine worked at an app used by a railway's personnel to know where to go next. The app was not particularly complicated but the backend, which has been running for ages, took a long time to run. I don't know the details.