A digital twin is a set of computer models that serve as a real-time digital counterpart of a physical object or process. The term was coined in the early 2000s in the context of Product Lifecycle Management (PLM)(1) to describe a set of computer representations of a product as it evolves through its lifecycle, from design to manufacture, then to operation, and finally to disposal. The digital twin was envisioned as an electronic repository of all aspects of design, such as 3-D CAD drawings and engineering models, in addition to operational descriptions such as bills of process. It is maintained throughout the product lifecycle via a real-time data stream of measurements obtained from the physical object. It is used to monitor and predict the behavior of the product in operation in its physical environment for diagnostic purposes, or in interrogative use cases in which past or future scenarios are analyzed to improve product design or operation.