This Recommendation | International Standard defines use of the Unified Modeling Language (UML 2.4.1 Superstructure Specification, ISO/IEC 19505-2, for expressing system specifications in terms of the viewpoint specifications defined by the Reference Model of Open Distributed Processing (RM-ODP, ITU-T Rec. X.901 to X.904 | ISO/IEC 10746 Parts 1 to 4) and the Enterprise Language (ITU-T Rec. X.911 | ISO/IEC 15414). It covers: a) the expression of a system specification in terms of RM-ODP viewpoint specifications using defined Unified Modeling Language (UML) concepts and extensions (e.g. structuring rules, technology mappings, etc.); b) relationships between the resultant RM-ODP viewpoint specifications. This Recommendation | International Standard refines and extends the definition of how Open Distributed Processing (ODP) systems are specified by defining the use of the Unified Modeling Language for the expression of ODP system specifications.