I think it all depends on the problem. If it is known how and what the code need to do, like transform the input in a particular way, then the data structures w

I think it all depends on the problem. If it is known how and what the code need to do, like transform the input in a particular way, then the data structures will naturally follow from actions. But if actions are not known or too abstract, like show a graph or create an app to calculate taxes, then defining data structures first will be beneficial as it allows to make actions more detailed.