Software engineering proposed the V-Model as an extension of the waterfall model. It is used by most industrial companies worldwide, not only in software engineering, but in any kind of engineering. There are three main difficulties that arise when humans want to understand and interact with a complex system. They need to know how the whole system works, why the system exists, and how it should be used. A digital twin (DT) is a virtual instance of a physical/cognitive system that enables to simulate dynamic phenomena of both structures and functions of a system. A DT can be used during the whole life cycle of a system. It can be used for support of training, operations, maintenance, and eventually dismantling. Active design document knowledge representation was initially developed to support traceability of design decisions, as well as rationalization of innovative concepts and incremental formative evaluations.