A Unified Knowledge Model for Managing Smart City/IoT Platform Entities for Multitenant Scenarios

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

*Overview*
Here, one can understand how entities of smart cities and IoT platforms could be managed with a focus on multitenancy management. Scientists have used the particular framework, the unified knowledge model, in smart city applications to overcome the problem of moving data from one system to another, handling a large amount of information, and expanding the reach of smart city services.

*Strengths*
*Innovative Approach: *In this sense, the management of a smart city is best represented by a unified knowledge model because it is an innovation in the area that enhances various aspects of a smart city and gathers them in one unified knowledge model that is useful in the field.
*Comprehensive Coverage:* In the following manuscript, some of the features and the operation of the proposed model, including the ingestion of the data and the processing and visualization of the processed data, are also described.
*Practical Application:* Real-life examples also help make the forecast and results numerically calibrated, making the overall research more valuable and usable.
The main weaknesses were identified as, well as recommendations mitigate them are as follows The main weaknesses that were identified, as well as recommendations to mitigate them, are as follows:
*Literature Review:*
Critique: Although the literature review section is exhaustive, it does not critically evaluate the existing models and frameworks. Namely, it mostly just enumerates other works in the sphere without properly discussing them compared to the proposed one.
Recommendation: Enhance the literature review by identifying the strengths and weaknesses available when applying the existing models. Highlight all key aspects explaining the absence of the proposed model in the literature and how it meets the existing deficiency.
*Methodology:*
Critique: As for the practical part of the research, it is still essential to make a critical comment: the sections proposed in the methodology and its literature review part are very scarce on the problem of the model’s implementation and its constructiveness. In this regard, it is unfortunate that the exact process followed to construct and test the proposed model is not described in detail.
Recommendation: Read more about strategies employed in the method section of the study regarding the procedures applied in the implementation of the study, data collection processes, and those that were applied to ensure verification of the study. See that you explain the algorithms/ tools used to create the model in detail.
*Technical Details:*
Critique: One disadvantage of the manuscript is that some sections written as subheadings, especially those concerned with the practical application of the model’s features, are too intricate and worded. The inclusion of technical language and the failure to provide or explain it makes it difficult for the reader to comprehend it.
Recommendation: It is recommended to use less technical terms and give clear definitions for technical terms in the areas of the book that are covered with higher technicality. Flowcharts and diagrams should be employed to drive home points and clarify concepts and processes.
*Case Studies and Results:*
Critique: The manuscript also contains case studies; however, the descriptions of the results and findings are insufficient. As much as the qualitative information supports the effectiveness of the model, there is a difficulty in quantifying the results of the model.
Recommendation: Expand on the case studies used by covering more details of the outcomes and the results achieved. Support all the propositions about the model’s efficacy with qualitative information and measurements alongside statistical measures. It is necessary to assess the proposed model according to certain benchmarks compared to existing models.
*Scalability and Interoperability:*
Critique: While the manuscript presents and stresses scalability and interoperability as the primary objectives, it lacks sufficient case studies or reviews of these aspects.
Recommendation: Include the specifics and assessments of how the model promotes scalability and interoperability. The last two are problems or limitations and expectations to overcome them or ways to work around them.

*Conclusion and Future Work:*
Critique: The final section is relatively short and does not provide an effective conclusion that would briefly outline the significant results and conclusion of the research. Further, the conclusion is followed by the Future Work section, which does not state clear guidelines for further study.
Recommendation: The conclusion above should be built to elaborate on the significant conclusions made in the study and the implications of the findings for the given field. Provide clear and detailed guidelines for future research, pointing to the probable areas of improvement and future research topics.
Overall Evaluation
In light of the above features, the presented manuscript offers a promising and novel concept of addressing the management and integration of competent city/IoT platform entities in multi-tenancy. If all the recommendations made herein are implemented, then the paper has the potential to impact the existing literature positively. I would like the authors to improve on the weaknesses noted to make their works easier to follow, more comprehensive, and significant contributions.

Comments on the Quality of English Language

The quality of the English language in the manuscript is good, but some areas can be improved to enhance clarity, readability, and professionalism. Here are some specific observations and suggestions:

Grammar and Syntax:

The manuscript contains a few grammatical errors and awkward phrasings that can be corrected with careful proofreading. For example:

"Therefore, Smart City operators in multitenant smart city infrastructures based on microservices in which the same data, processes/services and tools are cross exploited by multiple applications and developers." This sentence is incomplete and needs restructuring for clarity.

"The different data sources include IoT/IoE (Internet of Things/Everything) networks, open data portals, social media, private and/or public data, GIS (Geographic Information System), city utilities, industry plants, mobile apps, mobile cellular data, BIM (Building Information Modelling), census data, origin-destination matrices, etc., [6], [7], [8]." This sentence is overly long and complex. Consider breaking it into shorter sentences for better readability.

Punctuation:

Ensure proper use of punctuation, especially commas and semicolons, to improve the flow of sentences. For instance, some sentences are lengthy and could benefit from being split into shorter, more manageable ones.

There are instances where commas are missing before conjunctions in compound sentences.

Word Choice:

Some technical terms and jargon are used without explanation, which could confuse readers unfamiliar with the specific terminology. Ensure that all terms are defined upon first use.

Avoid redundant phrases. For example, "multitenant multiuser smart city infrastructures" can be simplified if the terms "multitenant" and "multiuser" are redundant in the context.

Consistency:

Maintain consistency in terminology and formatting throughout the manuscript. For example, decide whether to use "smart city" or "Smart City" and stick to one format.

Ensure consistent use of abbreviations. Once an abbreviation is introduced (e.g., IoT for Internet of Things), use it consistently.

Clarity and Conciseness:

Aim for concise writing. Some sentences and paragraphs are verbose and can be made more succinct without losing meaning.

Use active voice where possible to make sentences more direct and vigorous. For example, "The UKM has been developed..." is better than "UKM was developed..."

Paragraph Structure:

Some paragraphs are overly long and cover multiple ideas. Breaking these into shorter paragraphs focused on a single idea each would improve readability.

Proofreading:

 

A thorough proofreading by a native English speaker or a professional editor would help catch and correct minor errors and awkward phrasings.

Examples of Improvements

Original: "The new trends in smart city technology have been proposed by the introduction of integrated infrastructures and services [1]."

 

Improved: "New trends in smart city technology include the introduction of integrated infrastructures and services [1]."

Original: "A modern smart city infrastructure needs to support a multitude of data providers/consumers, several data exchange modalities, many data transformations and services which are executed on the same framework."

Improved: "Modern smart city infrastructure must support numerous data providers and consumers, various data exchange modalities, multiple data transformations, and services executed within a single framework."

By addressing these suggestions, the quality of the English language in the manuscript can be significantly improved, making the paper more polished and professional.

Author Response

*Overview*
Here, one can understand how entities of smart cities and IoT platforms could be managed with a focus on multitenancy management. Scientists have used the particular framework, the unified knowledge model, in smart city applications to overcome the problem of moving data from one system to another, handling a large amount of information, and expanding the reach of smart city services.

RESPONSE 1:Yes thanks.

*Strengths*
*Innovative Approach: *In this sense, the management of a smart city is best represented by a unified knowledge model because it is an innovation in the area that enhances various aspects of a smart city and gathers them in one unified knowledge model that is useful in the field.

RESPONSE 2:Yes thanks.

*Comprehensive Coverage:* In the following manuscript, some of the features and the operation of the proposed model, including the ingestion of the data and the processing and visualization of the processed data, are also described.

RESPONSE 3:Yes thanks.

*Practical Application:* Real-life examples also help make the forecast and results numerically calibrated, making the overall research more valuable and usable.

RESPONSE 4:Yes thanks.

The main weaknesses were identified as, well as recommendations mitigate them are as follows The main weaknesses that were identified, as well as recommendations to mitigate them, are as follows:
*Literature Review:*
Critique: Although the literature review section is exhaustive, it does not critically evaluate the existing models and frameworks. Namely, it mostly just enumerates other works in the sphere without properly discussing them compared to the proposed one.
Recommendation: Enhance the literature review by identifying the strengths and weaknesses available when applying the existing models. Highlight all key aspects explaining the absence of the proposed model in the literature and how it meets the existing deficiency.

RESPONSE 5: The paper has been revised in the direction your requested. The number of solutions minimally covering the innovation provided has been better described stressing their deficiencies, in Section 2.  Regarding the applications and processes’ point of view, ontologies modelling processes and their relationships have been defined in IoT scenarios, such as the Process-aware IIoT Knowledge Graph [62]. The IIoT Knowledge Graph does not address the problems related to managing multiple processes and solutions by multiple users on the same platform, exploiting the same data. Large-scale process data are increasingly addressed, especially associated to Industrial Big Data contexts, leading to the conceptualization and semantic description of Big Process [63]. However, these works have not yet been evaluated on real case studies and do not address the temporal queries related to IoT and Time Series. From the Service perspective, the Service Ontology Pattern Language (SOPL) has been presented in [64] and [65], providing the conceptualization of services as a network of interconnected ontology modelling patterns, allowing to build service ontologies in specific domains. However, this work is more focused on the concept of service among generic service providers and target customers (persons and organizations), without addressing entities and relationships related to the IoT and smart data models context. In [66], a lifecycle approach is proposed to model IoT-enabled smart city services as System-of-Systems (SoS), in order to overcome the vertical development of such systems into locked single domains. To this aim, Service Lifecycle Management (SLM) concept has been proposed and formalized through a Lifecycle Modeling Language (LML), which unfortunately does not provide an effective implementation and solutions to solve the above-mentioned problems due to multiple processes and solutions by multiple users on the same platform, exploiting the same data.

 

*Methodology:*
Critique: As for the practical part of the research, it is still essential to make a critical comment: the sections proposed in the methodology and its literature review part are very scarce on the problem of the model’s implementation and its constructiveness. In this regard, it is unfortunate that the exact process followed to construct and test the proposed model is not described in detail.
Recommendation: Read more about strategies employed in the method section of the study regarding the procedures applied in the implementation of the study, data collection processes, and those that were applied to ensure verification of the study. See that you explain the algorithms/ tools used to create the model in detail.

RESPONSE6 :The method to design the UKM is enforced in the paper. In the sense that, we analysed the state of the art looking for a solution to our identified requirements. The requirements are reported in Section 3. Then, a number of scenarios has been formalized, as those reported in Section 3 (just as examples). As a successive step we analysed the Snap4City platform and architecture to understand technical limitations and relationships among the actually involved entities, also observing the list of problems detected by the developers and managers in the recent years. This allowed us to classify them as related to applications, processes, operators and data flows. These concepts have been modelled into an ontology which has been refined by using a set of queries with inference to be sure to have modelled a solution which could be actually used for producing / inferring the answers to our questions.

This description has been included in the new version of the paper.

*Technical Details:*
Critique: One disadvantage of the manuscript is that some sections written as subheadings, especially those concerned with the practical application of the model’s features, are too intricate and worded. The inclusion of technical language and the failure to provide or explain it makes it difficult for the reader to comprehend it.
Recommendation: It is recommended to use less technical terms and give clear definitions for technical terms in the areas of the book that are covered with higher technicality. Flowcharts and diagrams should be employed to drive home points and clarify concepts and processes.

RESPONSE 7 :We hope that the graphic representation provided are those you requested. In more details, Figure 1 represents the main data flows among the smart city platform entities, Figures 2 and 3 are representing the data and control flows among modules in the smart city platform, Figures 5 and 6 are representing the ontological relations among the entities involved including the formal relationships in terms of triples. A total remake would be very heavy to be implemented in the short time at our disposal.

*Case Studies and Results:*
Critique: The manuscript also contains case studies; however, the descriptions of the results and findings are insufficient. As much as the qualitative information supports the effectiveness of the model, there is a difficulty in quantifying the results of the model.
Recommendation: Expand on the case studies used by covering more details of the outcomes and the results achieved. Support all the propositions about the model’s efficacy with qualitative information and measurements alongside statistical measures. It is necessary to assess the proposed model according to certain benchmarks compared to existing models.

RESPONSE 8 :we provided a qualitative and quantitative assessment (see table 1). Unfortunately, the problems addressed has not been addressed by other solutions, this makes impossible a comparison with existing models.

*Scalability and Interoperability:*
Critique: While the manuscript presents and stresses scalability and interoperability as the primary objectives, it lacks sufficient case studies or reviews of these aspects.
Recommendation: Include the specifics and assessments of how the model promotes scalability and interoperability. The last two are problems or limitations and expectations to overcome them or ways to work around them.
RESPONSE 9:As clarified in the new version of the paper, the numbers describing the context of the experiments as reported in section 7 provides the evidence of the usage of the solution in large scale conditions, and thus on the capacity of scalability of the UKM model proposed.
The interoperability has been only marginally mentioned in the former version of the paper. In the new version of the paper, we have clarified that Snap4City platform has been demonstrated to be interoperable being capable to cope with more than 150 protocols and formats. https://www.snap4city.org/65

*Conclusion and Future Work:*
Critique: The final section is relatively short and does not provide an effective conclusion that would briefly outline the significant results and conclusion of the research. Further, the conclusion is followed by the Future Work section, which does not state clear guidelines for further study.
Recommendation: The conclusion above should be built to elaborate on the significant conclusions made in the study and the implications of the findings for the given field. Provide clear and detailed guidelines for future research, pointing to the probable areas of improvement and future research topics.

RESPONSE10 :Conclusions have been improved and future work described. Future research activities are focused on organizing the artificial intelligence processes in execution and training by using MLOps approach. An extension of the UKM would be needed, and it will be grounded on a new version of theKm4City Ontology which is under development to cope with a larger set of complex data and more advanced Digital Twins.

Overall Evaluation
In light of the above features, the presented manuscript offers a promising and novel concept of addressing the management and integration of competent city/IoT platform entities in multi-tenancy. If all the recommendations made herein are implemented, then the paper has the potential to impact the existing literature positively. I would like the authors to improve on the weaknesses noted to make their works easier to follow, more comprehensive, and significant contributions.

RESPONSE 11:Thanks for your comments which helped us to improve the paper.

Comments on the Quality of English Language

The quality of the English language in the manuscript is good, but some areas can be improved to enhance clarity, readability, and professionalism. Here are some specific observations and suggestions:

Grammar and Syntax:

The manuscript contains a few grammatical errors and awkward phrasings that can be corrected with careful proofreading. For example:

"Therefore, Smart City operators in multitenant smart city infrastructures based on microservices in which the same data, processes/services and tools are cross exploited by multiple applications and developers." This sentence is incomplete and needs restructuring for clarity.

"The different data sources include IoT/IoE (Internet of Things/Everything) networks, open data portals, social media, private and/or public data, GIS (Geographic Information System), city utilities, industry plants, mobile apps, mobile cellular data, BIM (Building Information Modelling), census data, origin-destination matrices, etc., [6], [7], [8]." This sentence is overly long and complex. Consider breaking it into shorter sentences for better readability.

RESPONSE 12:thanks. The suggestions have been accepted and the changes applied.

Punctuation:

Ensure proper use of punctuation, especially commas and semicolons, to improve the flow of sentences. For instance, some sentences are lengthy and could benefit from being split into shorter, more manageable ones.

There are instances where commas are missing before conjunctions in compound sentences.

RESPONSE 13:The paper has been carefully reviewed.

Word Choice:

Some technical terms and jargon are used without explanation, which could confuse readers unfamiliar with the specific terminology. Ensure that all terms are defined upon first use.

Avoid redundant phrases. For example, "multitenant multiuser smart city infrastructures" can be simplified if the terms "multitenant" and "multiuser" are redundant in the context.

RESPONSE 14:thanks.

Consistency:

Maintain consistency in terminology and formatting throughout the manuscript. For example, decide whether to use "smart city" or "Smart City" and stick to one format.

Ensure consistent use of abbreviations. Once an abbreviation is introduced (e.g., IoT for Internet of Things), use it consistently.

RESPONSE15 :thanks, suggestions have been implemented in the new version of the paper.

Clarity and Conciseness:

Aim for concise writing. Some sentences and paragraphs are verbose and can be made more succinct without losing meaning.

Use active voice where possible to make sentences more direct and vigorous. For example, "The UKM has been developed..." is better than "UKM was developed..."

RESPONSE 16:thanks, suggestion has been implemented in the new version of the paper.

Paragraph Structure:

Some paragraphs are overly long and cover multiple ideas. Breaking these into shorter paragraphs focused on a single idea each would improve readability.

RESPONSE 17:The paper has been carefully reviewed, and improved according to your suggestion.

Proofreading:

A thorough proofreading by a native English speaker or a professional editor would help catch and correct minor errors and awkward phrasings.

Examples of Improvements

Original: "The new trends in smart city technology have been proposed by the introduction of integrated infrastructures and services [1]."

Improved: "New trends in smart city technology include the introduction of integrated infrastructures and services [1]."

Original: "A modern smart city infrastructure needs to support a multitude of data providers/consumers, several data exchange modalities, many data transformations and services which are executed on the same framework."

Improved: "Modern smart city infrastructure must support numerous data providers and consumers, various data exchange modalities, multiple data transformations, and services executed within a single framework."

RESPONSE 18:suggestions have been implemented in the new version of the paper.

By addressing these suggestions, the quality of the English language in the manuscript can be significantly improved, making the paper more polished and professional.

RESPONSE19 :suggestions have been implemented in the new version of the paper.

Reviewer 2 Report

Comments and Suggestions for Authors

The work developed presents a set of elements that should serve the concept of smart cities, alluding to a set of useful IoT tools for the development of cities. Also, the importance of data, its collection, is mentioned, so that it is possible to improve the processes to be developed and implemented according to the needs demonstrated in the respective cities.

A few things to note:

- The authors refer in the introduction to the importance of the infrastructures that support users/operators to have inaccurate data, coming from algorithms, communications and others. This is an important element that is expected that a universal solution per city typology can solve, that is, considering the same typology of services, communications, city geography, relationship with citizens, mobility, among others. Involving developers of systems and applications with different methodologies leads to error.

- The work proposal is: a Unified Knowledge Model, UKM, and framework for semantic reasoning and management of data and processes in a cross-network of micro - service applications that can be created in many different IoT/IoE-enabled smart cities with scenarios, exploiting the same data and tools of the Multitenant Multiuser Smart City Infrastructures.

- In view of the proposal presented, I understand that the objectives were achieved. However, I consider the following:

- The issue of collecting a large volume of data and developing machine learning algorithms for classification and forecasting, taking into account issues of mobility, temperatures, air quality, among others, was not taken advantage of. It was expected from the data that is collected and the added value for the cities.

- It is not understood how a set of cities, for example, belonging to the same region can have access to the same data and share, as well as allow users to access processes to be processed in different cities.

- An orientation guide for all those who visit a city, through the API, to guide them in matters of mobility, accessibility, use of digitization tools made available by cities.

- Sharing data across cities and with common services - such as location, sightseeing, leisure venues, business areas - these are elements that should be available on mobile devices automatically. It was important to have developed the API in this sense.

 

Author Response

The work developed presents a set of elements that should serve the concept of smart cities, alluding to a set of useful IoT tools for the development of cities. Also, the importance of data, its collection, is mentioned, so that it is possible to improve the processes to be developed and implemented according to the needs demonstrated in the respective cities.

RESPONSE 1:Yes thanks.

A few things to note:

- The authors refer in the introduction to the importance of the infrastructures that support users/operators to have inaccurate data, coming from algorithms, communications and others. This is an important element that is expected that a universal solution per city typology can solve, that is, considering the same typology of services, communications, city geography, relationship with citizens, mobility, among others. Involving developers of systems and applications with different methodologies leads to error.

RESPONSE2 :Yes thanks.

- The work proposal is: a Unified Knowledge Model, UKM, and framework for semantic reasoning and management of data and processes in a cross-network of micro - service applications that can be created in many different IoT/IoE-enabled smart cities with scenarios, exploiting the same data and tools of the Multitenant Multiuser Smart City Infrastructures.

RESPONSE3 :Yes thanks.

- In view of the proposal presented, I understand that the objectives were achieved.

RESPONSE4 :Yes thanks.

However, I consider the following:

- The issue of collecting a large volume of data and developing machine learning algorithms for classification and forecasting, taking into account issues of mobility, temperatures, air quality, among others, was not taken advantage of. It was expected from the data that is collected and the added value for the cities.

RESPONSE 5:The paper is grounded on the Snap4City platform which has the capability of collecting any kind of data, developing and exploiting AI for their exploitation, presenting data on dashboards, etc. The focus of the article is on the management of the infrastructure and on the fact that multiple data are used by multiple users in different tenants on the same infrastructure. The usage of multitenant platform is an advantage for saving costs, if the data and systems complexities are managed.

- It is not understood how a set of cities, for example, belonging to the same region can have access to the same data and share, as well as allow users to access processes to be processed in different cities.

RESPONSE 6:It is quite common that several cities belonging to same region/area would need to access at the same data. For example, for regional mobility infrastructure (they need to know the bus-stops in their location but also where the busses are going to arrive), from the regional telecom operator data as touristic origin destination data, from the same weather forecasts and quality of air data, from the same health data (triage hospital conditions), from the regional LIDAR data for terrain and land conditions, etc. These are the typical data collected and manged at regional/area level. In most cases, smart city processes need to access to those data and to download them to process them in local for their purpose, and regional operators may even not aware since they are distributed as open data. An integrated multitenant solution would reduce the costs and maintain the data usage clear for all, for producers and consumers, reducing duplications, make more efficient the update and distribution.

- An orientation guide for all those who visit a city, through the API, to guide them in matters of mobility, accessibility, use of digitization tools made available by cities.

- Sharing data across cities and with common services - such as location, sightseeing, leisure venues, business areas - these are elements that should be available on mobile devices automatically. It was important to have developed the API in this sense.

RESPONSE 7:we totally agree. In this sense, a plethora of vertical solutions could provide their own APIs with different authentications and mechanisms/formats. On the other hand, an integrated multitenant solution covering multiple verticals and areas would be much easier for the final users that would have all the services in a single Mobile App, with the same authentication in all the areas.  This is an advance also for web developers which would reach a larger groups of users with the same API approach and platform.

Reviewer 3 Report

Comments and Suggestions for Authors

The main idea of the submitted article is that an integrated framework (semantic Unified Knowledge Model) is needed for smart city operators using multitenant infrastructures based on numerous microservices, where shared data, services, and tools are utilized by multiple applications and developers. The framework will help in identifying problems and dysfunctions from their inception, assisting developers in reusing existing data and services to minimize costs and monitoring the work and resource usage of developers in a context where data and service reuse is common. While the practical part of the work is valuable and consistent, the Introductory and the Related work sections could benefit from increased clarity and conciseness. A more succinct and engaging introduction would enhance the overall readability and impact of the paper. 

Comments on the Quality of English Language

The paper also needs an extensive English review. Please find below some unclear phrases and typos (only for the very first part of the article).

Unclear phrases:

Lines 11-12: we addressed these 11 problems to provide at platform operators and developers effective models and tools to

Lines 42-43: To this end, service-oriented and microservices approaches are becoming diffusely adopted (?)

Lines 45-46: for which the physical entities are going have a

Lines 49-50: Thus, pushing towards the 49 Global Digital Twin concept [6]. The different data

Typos:

Line 34: mobile App

Line 54: , etc.,

Line 83: Paper Aim and structure

Line 91: missing )

Line 109: With the gool of

Occitanie and West Greece are not cities.

Author Response

The main idea of the submitted article is that an integrated framework (semantic Unified Knowledge Model) is needed for smart city operators using multitenant infrastructures based on numerous microservices, where shared data, services, and tools are utilized by multiple applications and developers. The framework will help in identifying problems and dysfunctions from their inception, assisting developers in reusing existing data and services to minimize costs and monitoring the work and resource usage of developers in a context where data and service reuse is common.

RESPONSE 1:Yes thanks.

While the practical part of the work is valuable and consistent, the Introductory and the Related work sections could benefit from increased clarity and conciseness. A more succinct and engaging introduction would enhance the overall readability and impact of the paper. 

RESPONSE 2:with the request received from all reviewers we carefully revised the whole paper.

Comments on the Quality of English Language

The paper also needs an extensive English review. Please find below some unclear phrases and typos (only for the very first part of the article).

Unclear phrases:

Lines 11-12: we addressed these problems to provide at platform operators and developers effective models and tools to

Lines 42-43: To this end, service-oriented and microservices approaches are becoming diffusely adopted (?)

Lines 45-46: for which the physical entities are going have a

Lines 49-50: Thus, pushing towards the Global Digital Twin concept [6]. The different data

Typos:

Line 34: mobile App

Line 54: , etc.,

Line 83: Paper Aim and structure

Line 91: missing )

Line 109: With the gool of

Occitanie and West Greece are not cities.

RESPONSE3 :They have been corrected.

Reviewer 4 Report

Comments and Suggestions for Authors

This article focuses on the weakness of single tenancy problem and build up the UKM to provide multi-tenancy system integration model. The initiatives are very good and important to the society but its aspect and other social concerns have been over-simplified or neglected.

1) This invention is the central brain connecting different devices together to aid the success of smart cities. But how about its security, fault-tolerance, contingency, latency, reliability, inter-operability, legacy system integrability? Especially the security concern, the whole smart city network would become paralyzed if one of the tenants is hostile or a hacker. What I can say the contribution of this article is just theoretically sound but practically none.

2) In system integration world, the usual method is through API or adapters. The authors have mentioned a little bit but the critiques are not sufficient to justify the cost to build up the UKM. 

3) Since there are many different integration standards from different big vendors in the whole world, I do not think they would join the proposed standard.

Comments on the Quality of English Language

The writing can be improved especially in the long and winding paragraphs. Some referencing are quite strange, e.g. the URLs were mentioned inside the article but not using citation method.

Author Response

This article focuses on the weakness of single tenancy problem and build up the UKM to provide multi-tenancy system integration model. The initiatives are very good and important to the society but its aspect and other social concerns have been over-simplified or neglected.

1) This invention is the central brain connecting different devices together to aid the success of smart cities. But how about its security, fault-tolerance, contingency, latency, reliability, inter-operability, legacy system integrability? Especially the security concern, the whole smart city network would become paralyzed if one of the tenants is hostile or a hacker. What I can say the contribution of this article is just theoretically sound but practically none.

RESPONSE 1:as explained in the paper, the multitenant platforms for smart city are a reality. Snap4City has many installations in this sense, and as explained in the paper, it is GDPR compliant and passed PEN test. Moreover, the multitenant approach in multiple installations is in place since a number of years without the problems you mentioned. See the list of installations on: https://www.snap4city.org/661

The adoption of multitenant approach for smart city leads to save money in: (i) developing data connectors, and adapting to new solutions, (ii) reducing data duplications and collecting new data for all, (iii) making possible the usage of “smart city as a service” approach, thus reducing the initial investment, (iv) reducing the risks for vendor lock-in on sensors and verticals, (v) reducing costs for maintenance, exploiting high experts for smart city applications, (vi) reducing costs in the control room support in which services need to be high available for early warning, (vii) reducing costs for planning tools, which are typically quite high and they are only used sporadically, with a central solution the costs will be shared among different cities.    

2) In system integration world, the usual method is through API or adapters. The authors have mentioned a little bit but the critiques are not sufficient to justify the cost to build up the UKM. 

RESPONSE 2:as above explained, the multitenant platforms for smart city are a reality, and one of the issues that allows to keep under control to control the costs in charge to a region for managing multiple cities is the availability of a UKM model and related tools.

3) Since there are many different integration standards from different big vendors in the whole world, I do not think they would join the proposed standard.

RESPONSE 3:yes of course there are several standard from vendors, mainly for sensors, vertical services, etc. It also true that each city has a different combination of services, sensors, etc., coming from different vendors, and thus the smart city control room platform for each of them has to be compliant with multiple standards as central platform, redeveloping again and again the same connectors. This is actually the job of horizontal multitenant platforms in integrating data from many sources, only once. If you have a single platform for several cities, you are saving money as above explained. This is what is doing Snap4City being capable to talk with more than 180 data protocol and formats, the save is much larger since all is open source, and limited to development of connectors once.

Comments on the Quality of English Language

The writing can be improved especially in the long and winding paragraphs. Some referencing are quite strange, e.g. the URLs were mentioned inside the article but not using citation method.

RESPONSE 3:thanks! done.

Reviewer 5 Report

Comments and Suggestions for Authors

The title of the article (2-3), although precise and up-to-date, unfortunately indicates too clearly that only one unified knowledge model can be formulated. In reality, it can only be a directional original concept of a variant of components of such a knowledge model, one of many treated equally. The synthesis of the most important findings (8-9), rarely found in the articles, seems too obvious, after all, corrective and preventive actions are the essence of effective management of each system (10-11), and sharing a data set in the BigData concept is crucial (15-16). This part disturbs the formal perception of the article and does not contribute much originality.

The “Abstract” section (17-31) correctly highlights the background of scientific considerations in terms of an integrated view of Smart City and IoT and indicates the goals (in short): identifying the causes, quickly linking them to data, and monitoring resources and programmers’ work. It also indicates the result in the form of the proposal of the “Semantic Unified Knowledge Model (UKM)” (25), which was validated on the open source Snap4City.org platform (28). This section is fully acceptable and compliant with the IMRaD standard. In the “Keywords” section (32-34) it is required to reduce the number of words (or rather phrases), avoid repetitions in the title and organize "from general to specific" in the context of the article's metadata focused on the main ideas.

In section “1. Introduction” (36-173) there is a very broad description of broad challenges for contemporary cities, extremely important and current, but often referred to only in slogans, e.g. “Digital Twin” (55), “smart city sustainability” (65) or “smart city infrastructure” (88). The background of the problem is outlined broadly, the most important elements of contemporary Smart Cities challenges are included, and the logic of the conducted scientific procedure (structure and layout of the article) is well presented. In section “2. Related Work” (174-297) he presents a number of examples (contributions) in which the IT perspective (with elements of information management) dominates, less related to city management. In section “3. Concepts and Requirements Analysis” (298-482) he presents “/…/Figure 1. Conceptual Architecture, from simple to Advanced Smart City/…/” with systematically presented and well-explained elements of the flow diagram within smart city applications and services. In the section “4. Snap4City Architecture” (483-524) there is primarily a description and an extensive graphical presentation of “Figure 4. Snap4City platform architecture” (505). In the section “5. Unified Knowledge Model” (525-691) the ontological idea of ​​the UKM model and the extremely important four research questions “/…/The most relevant competency questions defined were/…/” (542-547) are presented. The description of functioning and cause-effect relationships that follows in this part is interesting, although with such a title one could expect that the authors would present a graphic idea of ​​the UKM model with signaled example inputs “/…/in snap4City, the HLT concept is extended to many data types such as GIS data, BIM models, Traffic Flows, External Services, etc./…/” (682-683). The focus on functional usability is noticeable, not conceptual-methodological maturity, increasing the contribution of the epistemological theory to smart city management. Especially since in the "Introduction" section the authors themselves write "/.../The UKM has never been presented in other papers, despite of its implementation and validation in the context of the Snap4City framework (https://www.snap4city.org)/.../" (144-145). In the section “6. Exploiting UKM in Scenario 2 Analysis” (692-791) there is a successful presentation of the multi-faceted possibilities of user support, which clearly shows the high usability and functionality of the model environment thanks to the division into “/…/Accessing to UKM Model via Dashboards/…./” (708-739) and “/…/6.2. Accessing to UKM Model via Data Inspector/…/” (740-791). In the section “7. Exploiting UKM for Global Analysis” (792-891) the emphasis is put on “/…/the complexity and heterogeneity of use cases/…/” (793), providing a description of the relevant quantitative and qualitative arguments. The emphasis is put on “/…/Cohesion and exploitation among solutions and/or organizations/…/” (833) convincingly illustrating it with usefully relevant statistics that can be generated (Figure 8, Table 1). In section “8. Conclusions” (892-921) a synthetic description of the conceptual and application achievements was made “/…/The solution is currently in place on https://www.snap4city.org and accessible for its developers and it has been produced to cope with multiple interconnected scenarios in the context of Herit-Data/…/” (917-919). It is a pity, however, that the conclusions were not systematized and more fully extracted from the structure of the text. The article contains a list of 74 well-selected literature items, properly described with bibliographic notes and correctly used in the main text.

The article in its presented form is fully consistent with the main goals of "Smart Cities" (ISSN 2624-6511) and can be recommended for printing. All comments are of a more corrective nature, not reducing the substantive and formal value of the article.

Author Response

The title of the article (2-3), although precise and up-to-date, unfortunately indicates too clearly that only one unified knowledge model can be formulated. In reality, it can only be a directional original concept of a variant of components of such a knowledge model, one of many treated equally.

RESPONSE 1:we think that there space for more in fact the title state “A Unified Knowledge Model for Managing Smart City…..”, just one proposal.

The synthesis of the most important findings (8-9), rarely found in the articles, seems too obvious, after all, corrective and preventive actions are the essence of effective management of each system (10-11), and sharing a data set in the BigData concept is crucial (15-16). This part disturbs the formal perception of the article and does not contribute much originality.

RESPONSE 2:this part is the model the journal requested.

The “Abstract” section (17-31) correctly highlights the background of scientific considerations in terms of an integrated view of Smart City and IoT and indicates the goals (in short): identifying the causes, quickly linking them to data, and monitoring resources and programmers’ work. It also indicates the result in the form of the proposal of the “Semantic Unified Knowledge Model (UKM)” (25), which was validated on the open source Snap4City.org platform (28). This section is fully acceptable and compliant with the IMRaD standard.

RESPONSE 3 :ok.

In the “Keywords” section (32-34) it is required to reduce the number of words (or rather phrases), avoid repetitions in the title and organize "from general to specific" in the context of the article's metadata focused on the main ideas.

RESPONSE 4 :The keywords are those extracted from the main lists.

In section “1. Introduction” (36-173) there is a very broad description of broad challenges for contemporary cities, extremely important and current, but often referred to only in slogans, e.g. “Digital Twin” (55), “smart city sustainability” (65) or “smart city infrastructure” (88). The background of the problem is outlined broadly, the most important elements of contemporary Smart Cities challenges are included, and the logic of the conducted scientific procedure (structure and layout of the article) is well presented.

RESPONSE 5:thanks!

In section “2. Related Work” (174-297) he presents a number of examples (contributions) in which the IT perspective (with elements of information management) dominates, less related to city management. In section “3. Concepts and Requirements Analysis” (298-482) he presents “/…/Figure 1. Conceptual Architecture, from simple to Advanced Smart City/…/” with systematically presented and well-explained elements of the flow diagram within smart city applications and services.

RESPONSE 6:thanks!

In the section “4. Snap4City Architecture” (483-524) there is primarily a description and an extensive graphical presentation of “Figure 4. Snap4City platform architecture” (505).

RESPONSE 7 :ok.

In the section “5. Unified Knowledge Model” (525-691) the ontological idea of ​​the UKM model and the extremely important four research questions “/…/The most relevant competency questions defined were/…/” (542-547) are presented. The description of functioning and cause-effect relationships that follows in this part is interesting, although with such a title one could expect that the authors would present a graphic idea of ​​the UKM model with signaled example inputs “/…/in snap4City, the HLT concept is extended to many data types such as GIS data, BIM models, Traffic Flows, External Services, etc./…/” (682-683). The focus on functional usability is noticeable, not conceptual-methodological maturity, increasing the contribution of the epistemological theory to smart city management. Especially since in the "Introduction" section the authors themselves write "/.../The UKM has never been presented in other papers, despite of its implementation and validation in the context of the Snap4City framework (https://www.snap4city.org)/.../" (144-145).

RESPONSE 8:thanks!

In the section “6. Exploiting UKM in Scenario 2 Analysis” (692-791) there is a successful presentation of the multi-faceted possibilities of user support, which clearly shows the high usability and functionality of the model environment thanks to the division into “/…/Accessing to UKM Model via Dashboards/…./” (708-739) and “/…/6.2. Accessing to UKM Model via Data Inspector/…/” (740-791).

RESPONSE :thanks!

In the section “7. Exploiting UKM for Global Analysis” (792-891) the emphasis is put on “/…/the complexity and heterogeneity of use cases/…/” (793), providing a description of the relevant quantitative and qualitative arguments. The emphasis is put on “/…/Cohesion and exploitation among solutions and/or organizations/…/” (833) convincingly illustrating it with usefully relevant statistics that can be generated (Figure 8, Table 1).

RESPONSE 9:thanks!

In section “8. Conclusions” (892-921) a synthetic description of the conceptual and application achievements was made “/…/The solution is currently in place on https://www.snap4city.org and accessible for its developers and it has been produced to cope with multiple interconnected scenarios in the context of Herit-Data/…/” (917-919). It is a pity, however, that the conclusions were not systematized and more fully extracted from the structure of the text.

RESPONSE10 :The conclusions have been improved and future work described. Future research activities are focused on organizing the artificial intelligence processes in execution and training by using MLOps approach. An extension of the UKM would be needed, and it will be grounded on a new version of theKm4City Ontology which is under development to cope with a larger set of complex data and more advanced Digital Twins.

The article contains a list of 74 well-selected literature items, properly described with bibliographic notes and correctly used in the main text.

The article in its presented form is fully consistent with the main goals of "Smart Cities" (ISSN 2624-6511) and can be recommended for printing. All comments are of a more corrective nature, not reducing the substantive and formal value of the article.

RESPONSE 11:thanks a lot!

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

I am satisfied with the responses and changes although no time to check the mentioned sources about the practicality. Anyway, it is now an interesting professional article in such important area.