In this paper, we describe a comprehensive set of information constructs for representing Mixed and Augmented Reality contents. The proposed set of components extends the conventional ones used for representing virtual reality contents, as virtual environments are often used for Mixed Reality implementations. We lay out the principles and requirements for the proposed extension and give details of the component model including (but not limited to) those for place-holding the objects in the real world, sensors, extended events and behaviors, supporting video backdrops and specifying spatial calibration among the virtual and real. We demonstrate the ease and extendibility of our model with various examples and show partial implementation results. The proposed model will serve as a sound basis for establishing standard and interoperable mixed augmented reality contents in the future.