# A Categorization of Digital Twin and Model-Based System Engineering Interactions
## 3 Results
### Interaction Between DT and MBSE
The authors implemented loose coupling in their DT modeling to enable the simulation of variants. [PERSON] et al. [34] proposed an extension of the v-model for system development, which includes a model-in-the-loop, a twin-in-the-loop, and a system-in-the-loop. This is performed to develop smart products in a system of systems environment, where the SysML model created in the model-in-the-loop step is used to simulate the actual system, thus allowing the twin-in-the-loop to validate the DT during the development phase. Subsequently, the system-in-the-loop provides real-world data back to the development process, closing the loop. [PERSON] et al. [35] suggested an MBSE approach for the implementation of shop-floor DTs. They divided the implementation process into three domains: the problem, solution, and implementation domains. Each domain is characterized by its requirements, behavior, structure, and parameters. In their work, the authors adopted SysML as the modeling language, MagicGrid as the modeling method, and Camero Systems Modeler as the modeling tool. [PERSON] et al. [36] used MBSE to create master models for a family of products and their variants. These MBSE master models contain meta-information for the product, which is necessary to direct the production of the physical entity, as well as the DT. [PERSON] et al. [37] proposed the use of MBSE and mixed semantic modeling to create the architecture of a digital process twin. They suggested that this DT of a process can be composed of various individual equipment DTs, which provide data to aid in decision-making. The authors opted to use MetaGraph 2.0 as the architecture modeling tool and KARMA as the modeling language. [PERSON] et al. [17] presented a model-based approach to collaboratively specify DTs in their model-based digital twin design framework. The DTs can be broken down into systems of systems, systems, and subsystems, and, for each one, a DT is developed. The authors proposed the adoption of use cases generated by different stakeholders to achieve the collaboration needed to fully specify the DT. To facilitate this task, the authors suggested using their tool, the Digital Twin Specification Grid. This grid divides the DT into five layers: function, information, processing logic, data, and infrastructure. [PERSON] et al. [38] employed MBSE to construct a high-level DT and validate it in the early stages of development. The authors introduced a framework for the development of DT systems in a modular and loosely coupled architecture. This high-level DT is a lightweight model that can represent the overall behavior, physics, and structure of the physical counterpart. To model the DT, the authors utilized the UML enriched with Object Constraint Language (OCL) constraints. The modeling tool that they chose was USE, and they opted for the SOIL language to run the DT. [PERSON] et al. [39] proposed the Closed-Loop Engineering (CLOSE) methodology for the integration of EDTs and model-driven engineering processes. The methodology involves using MBSE to model the control logic of the system, which describes the overall behavior of the system. This information is then used by the DT to execute and simulate the system.