Semantic Definition Format (SDF) Modeling for Digital Twin

This memo specifies SDF modeling for digital twins, i.e. a digital twin systems, and their things. An SDF is a format that is used to create and maintain data and interaction, and to represent the various kinds of data that is exchanged for these interactions. The SDF format can be used to model the characteristics, behavior and interactions of things, i.e. physical objects, in digital twins that contain things as components.