I will need citation on which link, and how it defines ECS as a data structure.
From [1]:
> Entity component system (ECS) is a software architectural pattern. An ECS consists of entities composed of data components, along with systems that operate on those components.
From [2]:
> ECS ("Entity Component System") describes a design approach which promotes code reusability by separating data from behavior. Data is often stored in cache-friendly ways which benefits performance.
What you just described is a data structure that gets used. If the user brings the behavior what is the ecs? It's the data structure.
Of course it will be used somehow. I don't call a std::vector a "vector system" because someone uses it, but I guess people think using this data structure makes it a "system".
It's a data structure, except it doesn't describe how data is actually stored, only how its elements interact, so it's a data structure that doesn't actually structure data. If you are the kind of person that considers stuff like MVVM and Clean Architecture to be data structures, then I suppose it would be consistent. Most people don't.
It does store data so it is a data structure. Every implementation is meant to store data and the whole point is to have more memory locality so how it stores data is actually crucial.
No, not every ECS implementation is about data storage (to be more precise, component storage). This architecture's abstraction being better suited for data locality is the main appeal, yes, but many appreciate the mere separation of the GameComponent's Components into Components and Systems. So your assertion about it being strictly meant for data storage is just wrong. As [2] states:
> Data is often stored in cache-friendly ways which benefits performance.
Notice it says often, not always.
And bear in mind, generally, data structures aren't just about storing data. They are about storing data in a very particular way.
From [1]:
> Entity component system (ECS) is a software architectural pattern. An ECS consists of entities composed of data components, along with systems that operate on those components.
From [2]: > ECS ("Entity Component System") describes a design approach which promotes code reusability by separating data from behavior. Data is often stored in cache-friendly ways which benefits performance.