Let us say that I want to create a workout app and a website, the user enters his workout stats and the app display his stats with graphs percentage and such.
This is an example I don't want to create a workout app, just to understand how platforms work.
Assuming that I want to have an Android, iOS app and a website. All with the same functionalities.
From what I read, REST APIs are used for back end. This is an easy way of exchanging data between an app and the database. But what about operations on the data ?
Let us say I want to compute the average workout time (or something much more complex). Do I have to compute it on the device so create the algorithm 3 times (Android, iOS and web) or run all computations on the server ?
I tried to read the documentation of a REST api (Eve for Python) but I only found data operations like get update and delete.
Does REST APIs provides only data operation, is it possible to call a function or a script with a REST API ?
Maybe I misunderstood everything so could someone explain me how back ends works for a multi device platform ?