Rust (Bevy): ECS Network data structure

I am not quite sure if I completely understand the Entity Component System approach, and probably that is one of the reasons for the emergence of this question. Still struggling with the OOP mindset!

I am trying to create a data structure similar to a network, so for instance, something like a circuit:


So, for instance, entity 4 is connected to 1, 1 to 2, and so on. So far I have understood how to create the components, but I can't understand how the connectivity information should be stored. I believe that the entity should point to another entity?!? I have also imagined that would be even better practice to have a component that would have the connectivity information, but in that case, once again, what should it store? Ideally would be the entities themself, right? How to do it?

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