ITU-T Recommendation X.906 | ISO/IEC 19793 defines the use of the Unified Modelling Language (UML 2.1.1) for expressing the specifications of open distributed systems in terms of the viewpoint specifications defined by the Reference Model of Open Distributed Processing (RM-ODP). It defines a set of UML profiles for the expression of such specifications, and an approach for structuring them according to the RM-ODP principles. The purpose of this Recommendation | International Standard is to allow developers to use the UML profiles to write ODP specifications, and to allow UML tools to be used to process viewpoint specifications, thus facilitating the software design process. Annex A provides examples of the use of the UML profiles.