Mixed reality, natural user interfaces, and the internet of things converge towards an advanced sort of interactive system. These systems enable new forms of interactivity, allowing intuitive user interactions with ubiquitous services in mixed environments. However, they require to synchronize multiple platforms and various technologies. Their heterogeneity makes them complex, and sparsely interoperable or extensible. Therefore, designers and developers require new models, tools, and methodologies to support their creation. We present a unified model of the entities composing these systems, breaking them down into graphs of mixed entities. This model decorrelates real and virtual but still describes their interplay. It characterizes and classifies both the external and internal interactions of mixed entities. We also present a design and implementation framework based on our unified model. Our framework takes advantage of our model to simplify, accelerate, and unify the production of these systems. We showcase the use of our framework by designers and developers in the case of a smart building management system.