While there has been a recent growth of interest in the Digital Twin, a variety of definitions employed across industry and academia remain. There is a need to consolidate research such to maintain a common understanding of the topic and ensure future research efforts are to be based on solid foundations. Through a systematic literature review and a thematic analysis of 92 Digital Twin publications from the last ten years, this paper provides a characterisation of the Digital Twin, identification of gaps in knowledge, and required areas of future research. In characterising the Digital Twin, the state of the concept, key terminology, and associated processes are identified, discussed, and consolidated to produce 13 characteristics (Physical Entity/Twin; Virtual Entity/Twin; Physical Environment; Virtual Environment; State; Realisation; Metrology; Twinning; Twinning Rate; Physical-to-Virtual Connection/Twinning; Virtual-to-Physical Connection/Twinning; Physical Processes; and Virtual Processes) and a complete framework of the Digital Twin and its process of operation. Following this characterisation, seven knowledge gaps and topics for future research focus are identified: Perceived Benefits; Digital Twin across the Product Life-Cycle; Use-Cases; Technical Implementations; Levels of Fidelity; Data Ownership; and Integration between Virtual Entities; each of which are required to realise the Digital Twin.

尽管最近人们对Digital Twin的兴趣有所增长，但在整个行业和学术界仍采用了各种定义。有必要巩固研究，以保持对该主题的共识，并确保未来的研究工作要以坚实的基础为基础。通过对过去十年中92篇Digital Twin出版物进行系统的文献综述和主题分析，本文提供了Digital Twin的特征，知识差距的确定以及未来研究的必要领域。在表征Digital Twin时，将确定，讨论和合并概念，关键术语和相关过程的状态以产生13个特征（物理实体/双胞胎；虚拟实体/双胞胎；物理环境; 虚拟环境; 状态; 实现; 计量学; 孪生; 孪生率; 物理到虚拟连接/双绞线；虚拟到物理的连接/孪生；物理过程; 和虚拟流程）以及Digital Twin及其操作流程的完整框架。在此之后特征，为今后的研究重点7分知识差距和主题被确定：感知利益; 整个产品生命周期中的Digital Twin；用例；技术实现; 保真度; 数据所有权; 和虚拟实体之间的集成; 每个都需要实现Digital Twin。