From Digital Twins to Digital Twin Prototypes: Concepts, Formalization, and Applications

The transformation to Industry 4.0 also transforms the processes of developing intelligent manufacturing production systems. Digital twins may be employed to advance the development of these new (embedded) software systems. However, there is no consensual definition of what a digital twin is. In this paper, we provide an overview of the current state of the digital twin concept and formalize the digital twin concept using the Object-Z notation. This formalization includes the concepts of physical twins, digital models, digital templates, digital threads, digital shadows, digital twins, and digital twin prototypes. The relationships between all these concepts are visualized as class diagrams using the Unified Modeling Language. Our digital twin prototype approach supports engineers in the development and automated testing of complex embedded software systems. This approach enables engineers to test embedded software systems in a virtual context without the need of a connection to a physical object. In continuous integration/continuous deployment pipelines, such digital twin prototypes can be used for automated integration testing and, thus, allow for an agile verification and validation process. In this paper, we demonstrate and report on the application and implementation of a digital twin using the example of two real-world field studies (ocean observation systems and smart farming). For independent replication and extension of our approach by other researchers, we provide a laboratory study published open source on GitHub.