Digital Twin Conceptual Model within the Context of Internet of Things

Round 1

Reviewer 1 Report

The authors presented an interesting paper related to the appealing topic of Digital Twins. The objective of the manuscript is to present a conceptual model representing the replica of a physical object from the ground to the Cloud. According to me the topic is absolutely interesting for the reader, but that are still serious open issues that should be addressed by the authors:

• A detailed analysis of the State of the Art is missing. Several works have been published about digital twins and virtual replicas. The authors should highlight the existing approaches and how the proposed model is different. The same comment can be applied also to the application of DTs to the automotive field
• Following the previous point, the paper should better clarify the proposed contribution and innovation
• The methodology, presentation and validation of the model can be improved
• Is it the only available use case ?
• Is it feasible to validate the proposed approach through an experimental evaluation ?
• The presentation quality should be improved. The paper has only two figure (with a different style) and the core sections are completely text-only without any architectural o supporting figures helping the reader to follow the proposed approach and contribution.
• Conclusions should be improved

Author Response

Digital Twin Conceptual Model within the Context of Internet of Things

Dear Editor-in-Chief,

We would like to thank you for your quick and positive feedback on our paper. Also, we would like to thank the reviewers for their comments that we feel is an added value to our paper and has helped us improve the quality of our manuscript. We have carefully addressed the reviewers’ comments in the revised manuscript.

The following provides itemized responses to the reviewers’ comments and the changes are highlighted in blue in the revised manuscript. We would be happy to make further corrections if necessary and we look forward to hearing from you soon.

Thank you.

Prof. Al-Ali

Reviewer-1 Comments:

1. Comment-1: A detailed analysis of the State of the Art is missing. Several works have been published about digital twins and virtual replicas. The authors should highlight the existing approaches and how the proposed model is different. The same comment can be applied also to the application of DTs to the automotive field

Answer: We have added some more references in the literature review section. Papers 2-12 represent the application of digital twin in areas of smart farming, manufacturing industries. The proposed model is different from the existing work because it proposes an end-to-end conceptual model for a digital twin. On the other hand, most of the existing work in Digital Twins have focused only on the simulation aspect of the digital twin for emulating the mechanical process and the physical component of a machinery in the virtual layer of the architecture or the cloud. The proposed conceptual model incorporates different communication technologies, machine learning algorithms, as well as security for simulating a digital twin. These layers are essential for seamless integration of data in real-time from the physical layer up to the application layer encapsulated with a security framework for predictive maintenance. For example, our proposed digital twin model is used during the manufacturing and operation. In other words, the proposed Digital Twin collects the product’s real time operational data and surrounding environment parameters. For example, while a vehicle is on the move our proposed model can collect the real time operational parameters of the vehicle such as speed, ABS system, wheel pressure. Another example, it can monitor the vital signs of a human while he/she is on the move. Other existing digital twins deal with static objects, ours is dealing with static and dynamic objects.

2. Comment-2: Following the previous point, the paper should better clarify the proposed contribution and innovation?

Answer: Thank you for this comment. The proposed contribution and innovation has been modified in Section-2 Literature Review (paragraphs-4, 5, 6) of the revised manuscript.

3. Comment-3: The methodology, presentation and validation of the model can be improved?

Answer: Thank you for this comment. The changes are highlighted in blue in the revised manuscript in section-1 and section-2 of the revised manuscript. We have added some more references as well in Section-2 of the manuscript to complement our proposed work. Additionally, some more figures have been added in Section-8. Regarding the validation of the proposed model, we are working on it as a future direction for the proposed work.

4. Comment-4: Is it the only available use case?

Answer: Thank you for this comment. Another use case example with the proposed model is for smart healthcare patient monitoring system wherein the vitals of a mobile human can be monitored continuously from the physiological sensors attached to the human’s body. These sensors as well as human avatars will be replicated in the virtual space as digital twin and the data communicated from these sensors to the digital twin will help in making prediction on the status of human’s health in real-time.

5. Comment-5: Is it feasible to validate the proposed approach through an experimental evaluation?

Answer: Yes, it is possible to validate the proposed approach through an experimental evaluation. It is worth mentioning that with regards to the proposed use-case digital twin model for cars, some evaluation metrics that can be used are accuracy for predicting failures in the vehicular sensors in real-time, total latency and throughput for end-to-end communication from physical space to virtual space of digital twin and vice-versa, speed-up for the analytics model in the DAVL stage and scalability. This has been added in Section-7 of the revised manuscript.

We are in the pipeline towards implementing a test best for the proposed model to communicate live data from physical space sensors to virtual space digital twin with real-time sensing, communication and actuation for predictive maintenance of vehicles.

6. Comment-6: The presentation quality should be improved. The paper has only two figure (with a different style) and the core sections are completely text-only without any architectural o supporting figures helping the reader to follow the proposed approach and contribution.

Answer: We have added some more figures in Section-7 (Use-Case) in order to complement the read-only text in the document. Additionally, we believe that the tables in Section-3 and Section-4 should help supplement the related text in the manuscript as well.  

7. Comment-7: Conclusions should be improved.

Answer: Thank you for this comment. We have made necessary changes in the Conclusion section of the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

- Introduction is closer to Related Work than to a proper Introduction section. Research problem must be introduced. The methodology and the contribution must also be described (as well as other important part of Introduction). Related work needs a separate section.

- Figure 1 is not a concept model. If a concept model is the key result then it must be described and analyzed in detail in main sections of the paper.

- Sections 2-7 must explicitly define the proposed “digital twin conceptual model”. Now the sections do not provide a system (i.e., layers must form a concept model). Parametrized description is welcome since now only qualitative description is provided, which sometimes is unconcreted and ambiguous. By the way, is “digital twin conceptual model” (from Abstract) different from “end-to-end conceptual model for a digital twin” in Conclusion). Please use the same terms for the same concepts.

- Some sections are too short to form a proper section.

- Use-case analysis needs quantitative analysis. Provide size parameters and efficiency metrics to ground the properties of your concept model.

- More discussion on "smart or intelligence property" of digital twin is needed. For instance, consider "smart object" and "smart spaces" concepts from

 * https://ieeexplore.ieee.org/document/5342399

 * https://www.igi-global.com/book/ambient-intelligence-services-iot-environments/218560

 * https://ieeexplore.ieee.org/document/9082917/

Author Response

Digital Twin Conceptual Model within the Context of Internet of Things

Dear Editor-in-Chief,

We would like to thank you for your quick and positive feedback on our paper. Also, we would like to thank the reviewers for their comments that we feel is an added value to our paper and has helped us improve the quality of our manuscript. We have carefully addressed the reviewers’ comments in the revised manuscript.

The following provides itemized responses to the reviewers’ comments and the changes are highlighted in blue in the revised manuscript. We would be happy to make further corrections if necessary and we look forward to hearing from you soon.

Thank you.

Prof. Al-Ali

Reviewer-2 Comments:

1. Comment-1:  Introduction is closer to Related Work than to a proper Introduction section. Research problem must be introduced. The methodology and the contribution must also be described (as well as other important part of Introduction). Related work needs a separate section.

Answer: We have created a separate section for Literature Review in addition to the Introduction. The methodology and contribution have been highlighted in Section-1 Introduction (lines: 38-44) as well as in Section-2 Literature Review (paragraphs: 4, 5, 6) of the revised manuscript.

2. Comment-2:  Figure 1 is not a concept model. If a concept model is the key result then it must be described and analyzed in detail in main sections of the paper.

Answer: Fig. 1 has been modified in accordance to a generic end-to-end conceptual model of a Digital Twin for various applications in a Smart City.

3. Comment-3:Sections 2-7 must explicitly define the proposed “digital twin conceptual model”. Now the sections do not provide a system (i.e., layers must form a concept model). Parametrized description is welcome since now only qualitative description is provided, which sometimes is unconcreted and ambiguous. By the way, is “digital twin conceptual model” (from Abstract) different from “end-to-end conceptual model for a digital twin” in Conclusion). Please use the same terms for the same concepts.

Answer: Thank you for this comment. We would like to mention that this work is focused on an end-to-end conceptual model of a digital twin that encompasses different layers for sensing, communication, data aggregation and storage, 3D modeling, machine learning and analytics, visualization, application and security. Sections 2-7 of the revised manuscript elaborate on the latest and state-of-art technologies and techniques that can be used in each of these layers in the context of creation of a digital twin in the virtual space. We apologize for the ambiguity caused by the dual use of both terms, we have stick to using “end-to-end conceptual model for a digital twin” in the revised manuscript.

4. Comment-4:  Some sections are too short to form a proper section.

Answer: Thank you for this comment. With regards to short Section-6 (application layer) and Section-7 (security layer), it is in the preliminary stages and we are working on it as a potential future direction. However, since both application and security are a significant layers of the proposed conceptual model of the digital twin, we have tried to address this comment by combining both layers under a common Section -6 of the revised manuscript.

5. Comment-5: Use-case analysis needs quantitative analysis. Provide size parameters and efficiency metrics to ground the properties of your concept model.

Answer: For the Use-case example, we have referred to different physical sensors such as tyre pressure sensor, speed sensor, RADAR, GPS, sound sensor for the automobiles to capture real time parametric values from the vehicles and communicate them to the Virtual Space Layer in real time. The Virtual Space layer will communicate efficient control decisions to actuate the ABS, vehicle’s speed, steering control and motion planning. The proposed model is a conceptual model and we are going to test it in the future work to do quantitative analysis. In order to validate the performance of the proposed use-case digital twin model with cars, some evaluation metrics that can be used are accuracy for detecting failures in the vehicular sensors in real-time, total latency and throughput for end-to-end 5G communication from physical space to virtual space of digital twin and vice-versa, speed-up for the analytics model in the DAVL layer, and scalability. We have mentioned this in Section-7 of the revised manuscript. We believe that this is a useful comment and it will open future directions to our work.  

6. Comment-6: More discussion on "smart or intelligence property" of digital twin is needed. For instance, consider "smart object" and "smart spaces" concepts from

Answer: Thank you for this comment. We have added this in the revised manuscript as reference [10], [11], [12].

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

According to me the paper is improved and the authors followed the suggestions and comment of the previous review round. My main open points are related to:

- The difference between Figure 1 and 3 is to small. Remove Figure 3 or re-design it to provide a effective contribution to the paper

- The idea of the healthcare use case and application scenario is appealing and interesting both for the contribution and the readers. From my point of view it should be analyzed and presented within this paper in order to show how the presented model can be effectively applied to multiple scenarios. Furthermore, since the experimental evaluation of the first use can is not feasible at the moment a second analysis will give a great contribution to the paper

Author Response

We would like to thank you for your quick response on our paper. We would like to thank the reviewers for their comments that we feel is an added value to our paper and has helped us improve the quality of our manuscript. We have carefully addressed the reviewers’ comments in the revised manuscript. 

The following provides itemized responses to the reviewers’ comments and the changes are highlighted in blue in the revised manuscript. We would be happy to make further corrections if necessary and we look forward to hearing from you soon.

Thank you.  Prof. Al-Ali

Reviewer-1 Comments:

According to me the paper is improved and the authors followed the suggestions and comment of the previous review round. My main open points are related to:

Comment-1:- The difference between Figure 1 and 3 is to small. Remove Figure 3 or re-design it to provide a effective contribution to the paper.

Answer:  We have modified Fig. 3 with redesigning all digital twin model layers strictly with respect to its application in automobiles.

Comment-2:- The idea of the healthcare use case and application scenario is appealing and interesting both for the contribution and the readers. From my point of view it should be analyzed and presented within this paper in order to show how the presented model can be effectively applied to multiple scenarios. Furthermore, since the experimental evaluation of the first use can is not feasible at the moment a second analysis will give a great contribution to the paper.

Answer: Thank you for this comment. We have addressed this by demonstrating the application of proposed model in Smart healthcare monitoring system in Use-Case section with Fig. 5 and Fig. 6. The dataset for implementing this model will be extrapolated from [1]. The evaluation metrics for both Automobiles digital twin model and Smart Healthcare digital twin model remains the same.

Please see the attachment for the revised manuscript (in pdf) with updated description and figures. 

1. Al-Dmour J.A, Sagahyroon A, Al-Ali AR and Abusnana S., “A fuzzy logic-based warning system for patients classification”, Health Informatics J., vol. 25, no. 3, 2019.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript is improved after the revision. The last paragraph to Introduction should be added to describe the paper structure (sections).

Author Response

We would like to thank you for your quick response on our paper. Also, we would like to thank the reviewers for their comments that we feel is an added value to our paper and has helped us improve the quality of our manuscript. We have carefully addressed the reviewers’ comments in the revised manuscript. 

The following provides itemized responses to the reviewers’ comments and the changes are highlighted in blue in the revised manuscript. We would be happy to make further corrections if necessary and we look forward to hearing from you soon.

Thank you.  Prof. Al-Ali

Reviewer-2 Comments:

Comment-1:-The manuscript is improved after the revision. The last paragraph to Introduction should be added to describe the paper structure (sections).

Answer: We have appended the Introduction section with a brief description of paper structure in the revised manuscript.

Round 3

Reviewer 1 Report

I believe that the authors properly addressed the suggested comments and feedback and the paper can be accepted in the current form