>> The first sentence says that you must use object data structures to write OOP. Actually I don't think it does. It says that: "objects are data structures

>> The first sentence says that you must use object data structures to write OOP. Actually I don't think it does. It says that: "objects are data structures consisting of data fields and methods together with their interactions". There is no obligation. True it would be easier implemented in a language provided data-structure. But if you were crazy enough you could place the data-structure all in global variables and try to tie them up using reflection.