Despite best efforts, various challenges remain in the creation and maintenance processes of digital twins (DTs). One of those primary challenges is the constant, continuous and omnipresent evolution of systems, their user's needs and their environment, demanding the adaptation of the developed DT systems. DTs are developed for a specific purpose, which generally entails the monitoring, analysis, simulation or optimization of a specific aspect of an actual system, referred to as the actual twin (AT). As such, when the twin system changes, that is either the AT itself changes, or the scope/purpose of a DT is modified, the DTs usually evolve in close synchronicity with the AT. As DTs are software systems, the best practices or methodologies for software evolution can be leveraged. This paper tackles the challenge of maintaining a (set of) DT(s) throughout the evolution of the user's requirements and priorities and tries to understand how this evolution takes place. In doing so, we provide two contributions: (i) we develop DarTwin, a visual notation form that enables reasoning on a twin system, its purposes, properties and implementation, and (ii) we introduce a set of architectural transformations that describe the evolution of DT systems. The development of these transformations is driven and illustrated by the evolution and transformations of a family home's DT, whose purpose is expanded, changed and re-prioritized throughout its ongoing lifecycle. Additionally, we evaluate the transformations on a lab-scale gantry crane's DT.

翻译：尽管已付出最大努力，数字孪生（DT）的创建与维护过程仍面临诸多挑战。其中核心挑战在于系统、用户需求及其环境的持续、不间断且无处不在的演化，这要求已开发的DT系统必须随之适应。DT的开发具有特定目的，通常涉及对实际系统（称为实际孪生体AT）特定方面的监测、分析、仿真或优化。因此，当孪生系统发生变化（即AT自身改变或DT的范围/目的发生变更）时，DT通常需要与AT保持高度同步演化。由于DT属于软件系统，可借鉴软件演化的最佳实践与方法论。本文致力于解决在用户需求与优先级演化过程中维护（一组）DT的挑战，并尝试理解此类演化如何发生。为此，我们做出两项贡献：（i）开发DarTwin——一种支持对孪生系统及其目的、属性与实现进行推演的可视化符号表示法；（ii）提出一组描述DT系统演化的架构转换规则。这些转换规则的开发以家庭住宅DT的演化与转型为驱动案例进行阐释，该DT在其全生命周期中经历了目的扩展、变更与优先级重定义。此外，我们还在实验室级门式起重机DT上对这些转换规则进行了评估。