The "linked variables" concept is often called ["reactive programming"](https://en.wikipedia.org/wiki/Reactive_programming https://en.wikipedia.org/wiki/Reactiv

The "linked variables" concept is often called ["reactive programming"](https://en.wikipedia.org/wiki/Reactive_programming https://en.wikipedia.org/wiki/Reactive_programming) or ["data binding"](https://en.wikipedia.org/wiki/Data_binding https://en.wikipedia.org/wiki/Data_binding). And you're right that it's very helpful with GUI specification.