Comments
Invited Review Comment #169 Anonymous @ 2024-09-16 07:12
The work focuses on proposing a Digital Twin (DT) model tailored for distributed systems, with a key emphasis on enhancing communication between physical and virtual environments. The authors defined the components of their proposed model, highlighting the concepts of digital master and digital shadow. Then a case study from the GOLO archetype of the NFDI4Ing consortia were used to illustrate and evaluate how this DT model can be effectively applied in real-world distributed systems.
In my opinion the paper is well structured and the content is easy to read, forthermore tables and pictures support very well the reader. The exploration of a Digital Twin (DT) model for distributed systems is both crucial and intriguing due to the increasing complexity of modern industrial and engineering environments. As systems become more interconnected and diverse, the ability to seamlessly integrate and communicate between physical and virtual components becomes essential. This research addresses a significant gap by proposing a model that enhances such communication, which is vital for optimizing operations, improving efficiency, and enabling better decision-making in distributed systems. By focusing on the detailed characteristics and functionalities of digital masters and digital shadows, and validating the approach through a real-world case study, this work offers valuable insights into advancing DT technology and its practical applications, making it a timely and relevant contribution to the field.
However, it is important to acknowledge that legal aspects such as security and privacy are increasingly critical in today's technological landscape. Although these issues are not the main focus of this study, incorporating a brief discussion on how the proposed DT model addresses or impacts security and privacy concerns could significantly enhance the paper's value. Addressing these aspects would provide in my opinion, a more comprehensive understanding of the model's real-world implications, thus adding an important dimension to the overall contribution.
Invited Review Comment #122 Nico Kasper @ 2024-07-05 09:52
Dear Authors,
Thank you for your submission and contribution. I recommend a major revision of your paper and view this review as an opportunity to provide constructive feedback and an honest assessment. Engaging in a constructive discussion is always a valuable goal. My aim is to provide suggestions for improvement and direct you to additional sources that could enhance your work. I hope you find this feedback useful and use it to refine and strengthen your research. All comments are based on the sources listed below.
Although the topic of digital twins is relevant and offers a lot of research potential, I do not see the novelty in this paper. Most of the concept can already be found in general works and books such as Eigner 2021 and is covered by scientific literature (see below for sources). Also, the paper could benefit from a closer alignment with formal and content-related standards, as for example some sources don't fully support the statements made. Aditionally, the treatment of FAIR principles in the paper is quite brief and could be better integrated into the concept. Simply stating "this must work according to FAIR principles" repeatedly after each paragraph is not quite enough. Instead, I suggest integrating the FAIR principles into the overall framework and analysis of your research, clearly demonstrating how they are embedded within your methodology, concept and findings.
Formal aspects:
- Double space after the first sentence in the abstract.
- No explicit research question is provided. Adding this could help focus the study.
- The research gap is not highlighted. Highlighting the research gap would provide context for your study’s importance.
- The novelty of the approach is not presented. It would be helpful to clearly present what is new or innovative in your approach.
- Illustrations are often referenced after they are shown, not before. Make sure to reference illustrations before they appear in the text to guide readers more effectively.
The manuscript requirements are not met. The following points are missing:
- State of the art
- Methods (It is not clear what the research methodology is)
Content-related Feedback:
- I noticed a discrepancy in how the Digital Thread is defined. The paper describes it as merely a "bridge" between physical and virtual worlds and I disagree with the way this paper presents the concept of the Digital Thread. I also do not see that source 18 supports the definition of digital thread given in the paper, as the term digital thread does not appear in the source. It is not accurate to limit the Digital Thread to simply being a "bridge" between the physical and virtual worlds. In both industry-related and academic work, the Digital Thread is more commonly defined as:
"The Digital Thread connects the lifecycle phase-specific partial models of a Digital Model as well as the Digital Twin and its Physical Twin across the entire system lifecycle. It links the information and data of different processes and IT systems across the system lifecycle in a specific logical context. The Digital Thread is a framework of protocols and standards for interoperable and context-based connection and communication of different partial models and processes realized in different IT systems. It establishes an Authoritative Source of Truth across multiple systems."
The connection between the physical world and the virtual world has two separate dimensions that are initially independent of the digital thread. The technical level involves the protocols for transmitting information. This can range from manual data transfer to Wi-Fi, Bluetooth, or 5G. The logical level uniquely assigns the physical twin to the corresponding data set, typically accomplished using a unique ID, such as a serial number. Given that this is a central topic of the paper, I recommend conducting a thorough analysis and refining the concept to align with current scientific discussions. Specifically, the relationships between the Digital Master, Digital Twin, Digital Shadow, and Physical Twin should be clearly defined and articulated, with particular emphasis on how they interconnect through the Digital Thread. Additionally, the communication methods described at the end of the paper should be re-evaluated and categorized appropriately within this context. - Some definitions are not cloear, especially Digital Twin, Digital Shadow and Digital Master. Due to the range of possible definitions and the varying perspectives per discipline, a clear and precise definition is essential in the context of Digital Twins. These definitions should also be backed up with sources and derived from them. It is also important to distinguish the digital twin from simulation models without physical twins.
- The process of creating and a digital twin from a digital master is not well-defined. The terms BoM and BOP are used but not explained in enough detail. It is essential to distinguish between E-BoM and M-BoM. In general, the following sequence can be assumed in the automotive industry life cycle: Requirements -> Functional Structure -> Logical Structure -> Product Structure (e-BoM) -> BOP (Manufacturing processes) -> M-BoM (As-Built) -> As-Maintained. Sometimes, the M-BoM is derived from the E-BoM, and the BOP is created afterward.
- The paper doesn’t address how changes in the Digital Master affect the Digital Twin. Discussing this, especially in the context of variant management in the automotive industry, could add valuable insights. Specifically, it overlooks how the digital twin is referenced to the version of the digital master that is valid at the time of production. The configuration in which the digital twin was created is crucial in evaluating the data. In the automotive industry, variant management poses a significant challenge with digital twins. If focusing on a specific part of the automotive industry, it is strongly recommended to address these specific points.
- The contents of Figure 4 are inaccurate. It appears to be an Excel file that significantly reduces the complexity of Bills of Materials (BoMs) by essentially simplifying them to a list. However, this approach deviates from the traditional concept of a BoM, which is intended to encompass a comprehensive list of materials. Certain essential fields, such as material numbers or part numbers, quantities, and position numbers, are necessary for an accurate representation of a Bill of Materials.
- Figure 5 does not show a bill of process. The term is typically used for the manufacturing process. In particular, Siemens drives this definition with the Teamcenter and Digital Factory products. Therefore, the term BOP should be used accordingly in the context of the automotive industry.
Thank you for the opportunity to review your paper on digital twins. Your work addresses a highly relevant topic with significant research potential. However, to enhance the paper's contribution to the field, several improvements are recommended.
Firstly, ensuring that your discussion on digital twins and related concepts offers novel insights will strengthen your paper. Integrating FAIR principles more comprehensively and aligning your work with formal and content-related standards will also improve its scientific rigor. Clearer definitions, detailed methodologies, and accurate representations in your figures are crucial for clarity and precision. By addressing the feedback provided and incorporating additional sources, you can significantly enhance the quality and impact of your research. I look forward to your revisions and the further development of your valuable work.
Thank you again for your submission.
Please check these sources for further research:
Digital Thread
Bone, M., Blackburn, M., Kruse, B., Dzielski, J., Hagedorn, T., & Grosse, I. (2018). Toward an Interoperability and Integration Framework to Enable Digital Thread. Systems, 6(4). https://doi.org/10.3390/systems6040046
Eigner, M. (2021). System Lifecycle Management: Engineering Digitalization (Engineering 4.0). Springer Fachmedien Wiesbaden. ISBN: 9783658338732. https://doi.org/10.1007/978-3-658-33874-9
Gorringe, C., Gould, E., & Neag, I. (2023). Standards-Based Digital Thread as Authoritative Source of Truth. In IEEE AUTOTESTCON 2023 (pp. 1–10). IEEE. https://doi.org/10.1109/AUTOTESTCON47464.2023.10296125
Hedberg, T., Bajaj, M., & Camelio, J. A. (2020). Using Graphs to Link Data Across the Product Lifecycle for Enabling Smart Manufacturing Digital Threads. J Comput Inf Sci Eng., 20(1), Article 011011. https://doi.org/10.1115/1.4044921
Kraft, E. (2015). HPCMP CREATE;-AV and the Air Force Digital Thread. In 53rd AIAA Aerospace Sciences Meeting.American Institute of Aeronautics and Astronautics. https://doi.org/10.2514/6.2015-0042
Kwon, S., Monnier, L. V., Barbau, R., & Bernstein, W. Z. (2020). Enriching standards-based digital thread by fusing as-designed and as-inspected data using knowledge graphs. Advanced Engineering Informatics, 46(101102). https://doi.org/10.1016/j.aei.2020.101102
Digital Twin & Digital Model or Digital Master
Bleisinger, O., Psota, T., Masior, J., Pfenning, M., Roth, A., Reichwein, A., Hooshmand, Y., Muggeo, C., & Hutsch, M. (2022). Killing the PLM Monolith - the Emergence of cloud-native System Lifecycle Management (SysLM). https://doi.org/10.24406/publica-88
Eigner, M. (2021). System Lifecycle Management: Engineering Digitalization (Engineering 4.0). Springer Fachmedien Wiesbaden. ISBN: 9783658338732. https://doi.org/10.1007/978-3-658-33874-9
Kwon, S., Monnier, L. V., Barbau, R., & Bernstein, W. Z. (2020). Enriching standards-based digital thread by fusing as-designed and as-inspected data using knowledge graphs. Advanced Engineering Informatics, 46(101102). https://doi.org/10.1016/j.aei.2020.101102
Pfenning, M. (2017), “Durchgängiges Engineering durch die Integration von PLM und MBSE”, Dissertation, VPE, Technische Universität Kaiserslautern, 2017.
Singh, V., & Willcox, K. E. (2018). Engineering Design with Digital Thread. AIAA Journal, 56(11), 4515–4528. https://doi.org/10.2514/1.J057255
WIGeP, „Positionspapier: „Digitaler Zwilling“,“ Zeitschrift für wirtschaftlichen Fabrikbetrieb (ZWF), 2020, doi: 10.3139/104.112311.
BoM / BOP
Eigner, M. (2021). System Lifecycle Management: Engineering Digitalization (Engineering 4.0). Springer Fachmedien Wiesbaden. ISBN: 9783658338732. https://doi.org/10.1007/978-3-658-33874-9
Pfenning, M. (2017), “Durchgängiges Engineering durch die Integration von PLM und MBSE”, Dissertation, VPE, Technische Universität Kaiserslautern, 2017.
https://www.sw.siemens.com/de-DE/technology/bill-of-process/
Wardhani, R. and Xu, X. (2016), “Model-based manufacturing based on STEP AP242”, 2016 12th IEEE/ASME (MESA). DOI: 10.1109/MESA.2016.7587187
Xu, H.C., Xu, X.F. and He, T. (2007), “Research on Transformation Engineering BOM into Manufacturing BOM Based on BOP”, AMM, 10-12. DOI: 10.4028/www.scientific.net/AMM.10-12.99