Digital twin is a virtual entity that is linked to a real-world entity. Both the link and the virtual representation can be realized in several different ways. However, the ambiguous meanings associated with the term digital twin are causing unnecessary miscommunications as people have different interpretations of what can be accomplished with it. To provide clarity around the concept, we introduce a general approach to analyze and construct digital twins in various applications. We identify the common features of digital twins from earlier literature and propose an analysis method that compares digital twin instances based on these features. The method is used to verify the existence of the features and can be further enhanced. We formulate the observations to a feature-based digital twin framework (FDTF) to universally define and structure digital twins. The framework consists of three main principles: i) the idea that all digital twins consist of a definite set of features, ii) the features can be used to compare digital twin instances to each other, and iii) the features can be combined via a data link feature to construct future digital twins more efficiently. As key contributions, we found that the features can be identified in existing digital twin implementations and the feature combinations of the implementations are diverse. We suggest that the features should be leveraged to provide clarity and efficiency in digital twin discussion and implementation. We further propose a general procedure for building digital twins.INDEX TERMS Digital twin, enterprise systems, Industrial Internet of Things, cyber-physical systems.

The paper presents first experiences on an overhead crane platform targeted for university education, research, and innovation purposes. The main contributions feature a description of projects from the first year after the inauguration of the crane platform. To provide a basic perception on the potential of the platform, the paper presents the basic technical properties as well as opportunities and challenges of the crane platform. Digital Twin concept has been selected as a focus of the research activities on the platform. Hence, the paper reviews status of the term Digital Twin. Results describe experience-based observations on how university should manage an education, research, and innovation platform while collaborating with industry partners.

Industrial Internet of Things practitioners are adopting the concept of digital twins at an accelerating pace. The features of digital twins range from simulation and analysis to real-time sensor data and system integration. Implementation examples of modeling-oriented twins are becoming commonplace in academic literature, but information management-focused twins that combine multiple systems are scarce. This study presents, analyzes, and draws recommendations from building a multi-component digital twin as an industry-university collaboration project and related smaller works. The objective of the studied project was to create a prototype implementation of an industrial digital twin for an overhead crane called “Ilmatar”, serving machine designers and maintainers in their daily tasks. Additionally, related cases focus on enhancing operation. This paper describes two tools, three frameworks, and eight proof-of-concept prototypes related to digital twin development. The experiences show that good-quality Application Programming Interfaces (APIs) are significant enablers for the development of digital twins. Hence, we recommend that traditional industrial companies start building their API portfolios. The experiences in digital twin application development led to the discovery of a novel API-based business network framework that helps organize digital twin data supply chains.

Digital twins are expected to form a network, a "Digital Twin Web", in the future. Digital Twin Web follows a similar structure to the World Wide Web and consists of meta-level digital twins that are described as digital twin description documents and distributed via Digital Twin Web servers. Standards must be established before the Digital Twin Web can be used efficiently, and having an easily accessible server implementation can foster the development of those standards. Twinbase is an open-source, Git-based Digital Twin Web server developed with user friendliness in mind. Twinbase stores digital twin documents in a Git repository, modifies them with Git workflows, and distributes them to users via a static web server, from which the documents can be accessed via a client library or a regular web browser. A demo server is available at https://dtw.twinbase.org and new server instances can be initialized free-of-charge at GitHub via its browser interface. Twinbase is built with GitHub repository, Pages, and Actions, but can be extended to leverage other providers or self-hosting. We describe the underlying architecture of Twinbase to support the creation of derivative and alternative server implementations. The Digital Twin Web requires permanent, globally accessible, and transferable identifiers to function properly, and to address this issue, we introduce the concept of digital twin identifier registry. Performance measurements showed that the median response

No abstract