It might be a silly question, however, why are the computer systems in the X.200 model, OSI, called open systems?
Note that I've read that open system is defined as "the representation within the reference model of those aspects of a real open system that are pertinent to OSI" and the real open system is defined as "A real system which complies with the requirements of OSI standards in its communication with other real systems." in the X.200 specification.
Thanks in advance.