Amendment 1 to ITU-T Rec. X.904 | ISO/IEC 10746-4 refines and extends the ODP architectural semantics with a formalization of the computational language of the Reference Model for ODP. The computational language of the RM‑ODP provides for a description of ODP systems as collections of interacting objects. This Amendment formalizes the concepts and rules of the ODP computational language using different formal description techniques (LOTOS, SDL, Z and Estelle).