The fundamental difference between an ECS and a struct/object layout is that an ECS is column-oriented (aka columnar), while a struct/object layout is row-orien

The fundamental difference between an ECS and a struct/object layout is that an ECS is column-oriented (aka columnar), while a struct/object layout is row-oriented. Everything else about how you might query these layouts is more superficial... you can provide the same API with either layout, the same way you can in relational database systems (both layouts can be queried with SQL, but with different performance characteristics.)