Blockchain software design

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If we find out that the bug resides in the on-chain component of the system i. Software engineering researchers have already highlighted this problem Porru et al. In any case, undiscovered bugs could remain in the smart contract, and we have to manage such a situation during the software life cycle. Similarly, a situation might arise in which we need to add features to an already delivered BOS system Pinna et al.

Waiting to define the best practices for the maintenance of BOS, we identified two strategies to upgrade the on-chain component: A We could see the complete disposal of the current version of the smart contract and the deployment of a new version.

Contextually, all components of the system will be upgraded in order to replace the old smart contract address with the new one. B Design each smart contract to make possible its transforming into call forwarders. Practically, the current version of the smart contract will continue to receive calls from the other component of the BOS, but it will forward the calls to the new version of the smart contract. This strategy avoids the need of the upgrade of the other components of the system but requires more effort in the smart contracts design and implementation.

In summary, the sustainability analysis allowed us to elicit three additional non-functional requirements. The system should limit the number of blockchain transactions to the strictly necessary. The system User Interface must be user friendly and will have to support users in using the system features.

The on-chain component should include a maintenance procedure. We divided our BOS system in two main subsystems: the on-chain and the out-of-chain subsystems. The out-of-chain subsystem is responsible for the Web-based user interface. The on-chain system is the component stored and executed within the blockchain infrastructure and can be made of smart contracts. Figure 4 represents the main elements of the out-of-chain and on-chain systems.

In this paper, we focus mainly on the design of the on-chain subsystem. Figure 4. A representation of the BOS system in its two main components and of the communication channel between the two components. The out-of-chain component user interface interact with the on-chain component smart contracts by means of remote procedure calls through the blockchain.

We conceived our BOS to be decentralized and transparent. This means that we will design specific smart contracts to implement the specific Use Cases.

We can subdivide the Use Cases into three sets. The first set concerns functions and data, which directly involve the construction only. We organized data and functions in five main elements: the construction company, the OSP, the job, the worker, and the certificate. Figure 5 shows a class diagram to represent system elements as classes. It contains essential data and public functions of classes and represents the interconnections between system elements.

Figure 5. The high-level block diagram for the design of the interfaces of the on-chain component. The next step of the design iteration is the definition of Smart Contracts. From requirements, we learn that each OSP is the property of a construction company. At the same time, the construction company owns jobs and vacant jobs, contained in a given OSP. An OSP has a fixed structure and an owner who created it and who can modify its data.

Also, a job has a fixed structure and an owner. A non-fungible token is a digital element which belongs to a family of tokens which elements share the same structure but contains different data.

Using the library ERC, we can exploit well-implemented tokens which satisfy security requirements. We decided to implement OSPs and jobs as non-fungible tokens.

The ABCDE method proposes the use of specialized diagram and tables to provide a proper definition of smart contract-specific elements, such as the application binary interface, mapping, and function modifiers.

This diagram inherits the UML class diagram elements and adds some specific stereotypes. We use this diagram to define the public elements of the smart contracts and their structures. This smart contract implements requirements R1 and partially R2.

The construction company that creates a new OSP becomes its owner. The structure contains the information about the construction site required by the law and contains a list of jobs which characterize the working activity in the given construction site. The token IDs and data structures are linked through a map. Another map links construction company addresses to the list of OSP. Public elements will be visible to and callable from the out-of-chain components.

These elements will be written in the contract ABI application binary interface after compilation. Despite public visibility, we are able to prevent unauthorized executions of functions thanks to function modifiers. We define three modifiers which details are reported in Table 1. Figure 6. Its stereotypes represent the structured data contract and struct provided by the Solidity language.

This smart contract implements the list of requirements from R2 to R6, partially the R8, and from R9 to R This smart contract will be mainly used by two actors: the worker and the construction company. The construction company will create jobs to be connected to an OSP and will hire a worker for every single job. Of course, each worker and construction company are identified by their blockchain address. Figure 8 shows the sequence diagram of main interaction between smart contracts and the actors involved in job creation and in the hiring process.

The diagram focuses on the logical sequence of operation. It collects the abovementioned status, the identifier of the OSP it belongs to, the job details, according to the legal requirements of the OSP, the address of the hired worker, and the address array of applicants.

Each job is thus identified in the contract by a unique numerical ID that represents each token in the contract. The job can be assigned to a hired worker or vacant. The list of public functions includes several getters to return jobs data given its identifier.

In general, getters should be free while setters and every function which modify stored data inside the blockchain should incur an execution cost. To rule the function execution the smart contract includes four function modifiers of which Table 1 describes the actions. Figure 7. Figure 8. Thanks to the ABI contents, the user interface will be able to call remotely the public functions of deployed smart contracts.

By defining the ABI through the contract diagram, it is possible to start in parallel both the implementation of smart contracts and the web component. Finally, we can add that, to protect workers' privacy, personal data must be recorded apart in a dedicated smart contract. In our system, OSP data include only the Ethereum address of the worker. According to literature results described in section 2, there are several options to implementing a trusted privacy system for managing the personal and professional data of workers.

Well-organized User Interfaces, which take into account the requirement R14, complete the decentralized application. To meet requirement R14 for ease of learning and user guidance, we have divided the interface into four modules, as represented in Figure 9 , one for each type of actor in the system.

In this way, each actor will only see the functionalities that belong to them. The modules contain specific functions for the type of user they are addressed to. The functions of user interfaces are designed to enable the easy interaction with the corresponding smart contract functions. User interfaces implementations share two ABI files, that we represented in the box in the center of the diagram, connected with a dashed line to the corresponding smart contract.

These files are essential for the communication between the out-of-chain and the on-chain components because they contain all public function and variable names of the smart contract and the expected input and output types. Figure 9. Block diagram of the elements of the web-based user interfaces. The stereotype. The four. The implementation of the BOS system for building workers includes the writing and the deployment of the smart contracts and the writing and the publishing of web-based user interfaces.

In addition, the implementation includes the unit tests to find vulnerabilities and bugs, and the acceptance tests to asseverate the correct implementation of the system features, previously described as requirements. We implemented the on-chain component of the system using the blockchain Ethereum, a famous and widely used platform for decentralized applications.

We have chosen Ethereum for three reasons. Firstly, Ethereum is a decentralized blockchain, without obstacles at the entrance, and it is supported by a large peer-to-peer network.

Secondly, the development environment is also continuously updated, both for what concerns the programming language specifications solidity and for the existence of tools for testing and code quality evaluation. Finally, Ethereum is actually the most popular; it is tested and supports a flexible programming language for writing smart contracts.

If the smart contract compiles correctly, the IDE produces the bytecode that will be deployed in the blockchain and the associated ABI, which contains the names and the interfaces of public variables and functions. Our smart contracts inherit the the ERC smart contract provided by Openzeppelin on GitHub, which enforce the satisfying of security requirements. We tested the behavior of our smart contract by means of the definition of the expected behavior, described as UML sequence diagrams.

The testing phase allowed us to systematically individuate incorrect behavior and fix it. To limit the cost of the transactions, some adjustments in the structure of contracts simplified and decreased to the essential interactions between the two contracts.

For the same reason, we configured the setters of OSP and job tokens as atomic. In our implementation, a single function allows the filling of all token details at once.

This limits the number of transactions that the construction company has to send to the contracts to publish its OSP. We studied the strategy to allow the update of the smart contracts, in a simple, cheap, and secure way. We implement the replacement of a smart contract by means of a deactivation function. To allow the deactivation of the smart contract we implemented an enum-type variable with two tags.

Only the System Owner can deactivate the smart contract and that only if a new version is already deployed. After the deactivation, the old contract allows the reading of stored data but avoids any modifications. Thanks to the definition of function modifiers, we can write a specific set of requirements only once for a given set of functions.

They also avoid the writing of the same execution control such as the keyword require in several functions. For instance, all the functions that modify the OSP data could be executed only by the construction company who create it. So, the modifier onlyOSPowner inputs the id of the token OSP we want to modify and checks whether the sender of the transaction called msg.

If the two addresses do not match, the body of the modifier blocks the execution. Specific importance takes also the token ERC, which allows to assign an owner to each token and to authorize a specific address in our chase the smart contract address to manage the same token.

For what concerns the implementation of the out-of-chain component, we implemented the web-based user interfaces in the Html and javascript languages, by using the libraries jQuery and Bootstrap to define graphical elements and their behaviors, and the library web3. The library web3.

A mobile version of metamask is currently under development. We estimated the cost of the use of smart contracts and of the interaction with the Ethereum blockchain. The deployment of the smart contracts is the most expensive operation. Creating a new token OSP costs , units of gas about five dollar cents , and the filling of OSP data without workers costs , unit of gas. Add a job position costs , units of gas and filling job data costs , unit of gas.

Hiring a worker costs only 78, unit of gas. Smart contract return formatted data to be presented in the user interface. Figure 10 shows a screen of the user interface which presents OSP data. The screen shows the same data reported in Listing 1. Figure In this section, we evaluate our design choices in terms of the BOS system for the management of workers in construction sites.

We will analyze some aspects elicited from the sustainability analysis and others from the implementation phase. Finally, we will compare our system with a successful case of a platform for managing workers in construction sites, namely, the French Bativigie platform.

Our system focuses on safety requirements that the construction company must perform. The system provides a fast and transparent procedure to publish safety documents and allows an easy and trusted procedure to verify the correctness of documents by labor inspectors.

This is a desired and crucial effect of the system that in turn leads to several enabling and structural effects. One of these is the reduction of government costs for inspections due to digital and always available documents, not only regarding the construction site but also the presence of workers in the site. The labor inspectorate can set up a supervision strategy to generate alerts in case of anomalies in the data flow and to decide to perform on site controls.

We also expect that construction companies which use the BOS system for building workers have a competitive advantage because they should look more attractive to the Site Owners. This because a construction company which uses the system is certainly a more reliable and modern company. As a consequence, an increase in site owners choosing virtuous companies due to the decrease in injury at work is expected. This is a structural effect that brings attention to worker safety, but it also leads to a reduction in costs for injury at work.

Another structural effect which concerns the environmental dimension is the reduction of building abuses. The more companies use the system, the fewer companies will be willing to build outside the law.

In addition, virtuous companies can connect the BOS for building workers with a blockchain-based tracking system for dangerous construction materials and for waste management. Construction and Demolition Waste Management CDWM includes several aspects, such as those social, environmental, economic, institutional, and political, by dealing with technology, engineering, management, legislation, and policies. According to Ratnasabapathy et al. Proper management of construction materials is mandatory for the safeguarding of the environment and also for the health of workers.

In terms of the technical dimension, we already paid attention to the need of a well-organized user interface to break possible barriers at the entrance. We can add that the existing Tax Assistance Centers could play a facilitating role for those who have no knowledge of blockchain technology.

New appropriately trained staff will be able to guide the construction company in creating a blockchain address, purchasing cryptocurrency and purchasing OSP tokens. In addition, the use of the system leads to a remodeling of the role of employment centers and temporary agencies, creating a more direct relationship between construction companies and workers and a cost reduction. As mentioned, in this study, we implemented the system's smart contracts as non-fungible ERC tokens.

We adopted the concept of code reuse to save time and effort both in smart contract design and their implementation and to exploit publicly available state-of-the-art implementations of ERC tokens, which include last Solidity security recommendation and efficiency patterns.

However, there are different specializations and extensions of non-fungible tokens, which allow for simplification of the implementation of certain types of smart contract systems see for instance ERC and ERC For the purposes of this research, these do not offer features that make them preferable. As described in section 3, a number of digital platforms exist in the market to enhance the labor market or to manage recruitment and payment of workers. Among them, we have chosen to compare our system with Bativigie for two reasons.

The first is the need to compare the features of our proposal with those of a complete and well-used system. The second is the need to evaluate the implications and potential effects of our system with those of a system operating in the same domain.

Bativigie is a well-documented software system that is currently in use and operating in the domain of safety and temporary work in building. In the following, we subdivided our comparison into five sections that represents the five dimensions of sustainability. Our system and Bativigie share the common goal of making the hiring of workers at construction sites easier, in full compliance with applicable laws, and making available for labor inspections information about working relationships.

It provides a tool for site owners or their delegate in order to facilitate the supervising role that they must take in the construction site by law. This system allows for the construction site's registration in the system and employment management. In addition to this, our system allows construction companies to add vacant positions and workers to apply for job offers.

In this way, construction companies can find autonomously qualified workers. Thanks to blockchain technology, our system improves transparency and trust of building work relationships, including work agreements and safety prescriptions. This improves the trust between workers and employers, makes labor inspection trustworthy, and improves the relationship between the State and construction stakeholders.

Both systems lead to the direct effect of increasing worker safety thanks to the creation of regular contracts and compliance with workplace safety laws. In Bativigie, construction companies add workers to the construction site data within the system.

A specific section allows the hiring of temporary workers. Workers can access their report and personal data, which are stored in the Bativigie server. Our system is designed to improve worker agency. It allows each worker to create their profile and to become an active player.

Workers can add competencies, professional qualifications, and experiences. In our system, all personal data are property of the worker, and they can make their profiles available for use by the construction company. Bativigie is a typical client-server system.

A centralized database stores construction site data, and a specific permission handler allows a third party to read the stored data. By contrast, our system is decentralized and blockchain based. This is a key factor for two reasons. The first is due to the nature of the blockchain-based system. There is no central organization to which the actors of the system must refer apart from the acquisition of the token, as explained below. Furthermore, the system cannot be interrupted since it will always be accessible as long as there are active nodes in the blockchain.

The second concerns the fact that the ownership of the data is completely reserved to its owner, identified with a blockchain address. For example, construction companies own their OSP tokens, workers own their personal data, etc. Owners of the data will allow third parties to read or modify them.

To make easier the use of the system, Bativigie provides a mobile application with which the construction company can report any event that occurred on the construction site that affects workers, such as accidents and the like, and store results inside the database.

Our BOS allows the construction company to verify the presence of a given worker at the construction site and record it in the smart contract through the web interface. Labor inspectors can read data stored in the blockchain to check regularity. For what concerns the business model, Bativigie requires the payment of a fee if which the amount depends on the value of the construction site and on the size of the construction company.

In our case, the business model is based on selling the OSP and on job tokens. We can define a price for an empty OSP token and a price for an empty job token. In this way, the total price of the use of the system will have a fixed fee plus a variable fee, which depends on the number of workers on the construction site.

A centralized system like Bativigie has a systemic carbon footprint due to the IT architecture and company organization. Conversely, as previously discussed, our BOS system has a carbon footprint that depends on the volume of transitions performed and on the characteristics of the blockchain protocol.

In the long term, the two systems can both lead to environmental protection. Thanks to a simplification of inspection process, there will be a possible reduction in construction abuse and the possibility of reducing the overall carbon footprint of the construction sector. In this work, we presented a software system for the management of temporary employment of Building Workers and Construction Companies based on the blockchain technology that natively supports decentralization, transparency, security, and tamper proof.

The advantages provided by this technology with respect to similar centralized software systems are transparency for labor inspectors, data integrity and immutability, tamper-proof time stamps for registering any activity, and the decentralized execution of smart contracts that automatically implement contract clauses respecting legal requirements in the domain field.

Focusing on the Italian case, we included the implementation of the OSP Operational Safety Plan into the system's requirements so that legal policies about safety at the building site are automatically implemented through smart contracts.

We corroborate the system with a sustainability analysis in five dimensions that enables an a-priori evaluation of the impact of the approach and contributes to the requirements analysis since the very beginning in order to avoid pitfalls and mistakes in the future system development. We also analyzed by means of UML Contract Diagrams the interactions and the data structure of the Smart Contracts developed and deployed in the blockchain.

The solution is available for workers and construction companies as a decentralized web application. We performed an analysis of the practical usage of our systems and computed the costs of use. Our results show the feasibility of the approach with reduced costs, enhanced transparency, and security.

The proposed system represents a way to meet the current legal requirements relating to the documentation on worker safety on construction sites, managing them in a dematerialized and decentralized way. It is also a tool for the construction company that allows the selection of candidates, monitoring the work done and keeping track of costs, simplifying the bureaucracy related to temporary hiring.

The datasets generated for this study are available on request to the corresponding author. AP conceived the original idea and performed the sustainability analysis. GB performed the state of the art and the analysis of study cases. AP and GB drafted the manuscript. RT contributed to the final version of the manuscript. MM and RT supervised the project. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Alestra, L. Ispettorato Nazionale Del Lavoro. Al-Htaybat, K. Global brain-reflective accounting practices. Bach, L. Beck, K. Manifesto for Agile Software Development. Available online at: www. Google Scholar. Becker, C. Requirements: the key to sustainability. IEEE Softw. Caruso, A. Destefanis, G. Diginex Duboc, L.

European Construction Sector Observatory Analytical Reports. Proposing the use of blockchain to improve the solid waste management in small municipalities. Heiskanen, A. The technology of trust: How the internet of things and blockchain could usher in a new era of construction productivity. Hijazi, A. Inail Jeong, W. Design of recruitment management platform using digital certificate on blockchain. Liyuan, L. Marchesi, M. Michaelides, M.

The challenges of ai and blockchain on hr recruiting practices. Cyprus Rev. Nguyen, Q. Onik, M. Peisl, T. Penzenstadler, B. Software engineering for sustainability: find the leverage points! Penzes, B. Blockchain Technology in the Construction Industry: Digital transformation for high productivity. Technical Report. CrossRef Full Text. Perera, S. Blockchain technology: is it hype or real in the construction industry? Pinna, A. A massive analysis of Ethereum smart contracts empirical study and code metrics.

IEEE Access 7, пїЅ Porru, S. Ratnasabapathy, S. Sandanayake, S. Gunatilake, and A. Waidyasekara Colombo , 45пїЅ Saberi, S.

Blockchain technology and its relationships to sustainable supply chain management. Sarda, P. How should a dApp be designed and curated to be truly efficient? API management, architectural capabilities, system integration, transformation and connectivity, security performance and resilience пїЅ there are far too many variables to comprehend. Taking the lead, this insight explains the fundamentals of architecture design for blockchain applications in order to help startups and enterprises understand dApps as reliable and stable enterprise-grade solutions.

Centralized apps are more private in the sense that data stored within them can be made public or private at the discretion of the single entity that owns that specific application. To put it another way, users have little to no control over the data collected by centralized apps. When it comes to transactions, centralized applications are faster because it requires only reaching out to one system to get that single transaction completed. Because centralized apps require fewer resources, they are less expensive.

Decentralized applications are more transparent than centralized applications because multiple stakeholders can participate in the entire network through their nodes, and the data is available to every node or stakeholder. Whatever information stakeholders want to make public, they can do so. Decentralized apps are maintained by multiple stakeholders, each of whom has a say in the consensus of the actions facilitated by the app.

The percentage varies depending on the platform. So, the fundamental difference between centralized and decentralized apps is that centralized apps are managed by a single entity, whereas decentralized apps are managed by a network of participating stakeholders, all of whom have equal access to the data. Data is verifiable and trustworthy here. Several layer one protocols have emerged in recent years.

These protocols serve as the foundation for dApp development, and then there is the ecosystem for building apps or products on top of it. The ecosystem and its SDKs, tools, and utilities assist the developer community in building products on top of the layer-one protocol. Swap is an on-chain application that allows the exchange of one token for another within the same network.

Bridges are on-chain applications that connect two layer-one protocols or blockchains. Decentralized exchanges are online platforms for a cryptocurrency exchange that allow direct peer-to-peer cryptocurrency transactions without the use of an intermediary.

Analytics platforms are essentially performance dashboards built on-chain to display data from these chains, primarily network data such as network speed, active nodes, number of blocks created, speed of file retrieval, and so on. Browser extensions: Some analytical platforms are typically off-chain in nature.

Chrome extensions, for example, or browser extensions. Though they are off-chain products, they communicate with the network primarily through the web3 protocol, allowing users to read and write through extensions. Explorer: This product allows users to explore the entire blockchain network, see what activities are taking place, and keep track of various transactions. So, an explorer is a window or interface that allows users to view a network.

Metaverse is essentially a virtual world with digital 3D assets that users can interact with to enhance their digital experiences. Having 3D assets is one component of a metaverse project, however, there are other components. Take the example of a gaming metaverse. Along with 3D assets, another important component is the gaming engine, which serves as the foundation for the gaming or virtual environment. In a decentralized metaverse, blockchain stores all the meta-information around assets and their transactions.

It facilitates transactions and trade-offs based on various events. Decentralized Metaverses have a hybrid environment; for example, metaverse marketplaces for NFTs are hybrid, despite the fact that the majority of the work is done on-chain.

Also, there is data that is stored in multiple locations, on-chain as well as off-chain. As we discussed some examples of enterprise and consumer-focused DApps in the above section, we can divide dApps into four categories:.

These are used to keep health records, supply chain records, land records, and so on. Blockchain is increasingly being used by businesses to create these record-keeping or data-keeping applications. Many businesses are exploring the idea of digitizing their assets for a variety of reasons.

Some want to develop their intellectual property, while others require it for loan staking and other purposes. As a result, enterprises are developing blockchain applications to achieve asset digitization, which is occurring not only in the enterprise but also in the consumer space. There are multiple businesses flows in the business world, and the workflow of each department overlaps with the other department at various touchpoints.

Then there are multiple stakeholders at various levels. A decentralized workflow application is more of a business flow management application that attempts to bring together different stakeholders at various stages so that they can coordinate with each other in a transparent, trustless manner. They can, for example, sign documents and store them on the Blockchain.

The insurance industry processes insurance claims using blockchain decentralized workflow apps, as blockchain improves data trust. There are numerous decentralized workflow use cases in insurance and claim management, among other areas. There are a variety of consumer-focused decentralized finance applications available, including peer-to-peer lending platforms, crypto loan platforms, exchanges, and staking platforms.

Other consumer-focused blockchain applications include voting apps and loyalty programs. Consider the following scenario: you are attempting to create a Blockchain-based aircraft maintenance record-keeping application.

Perhaps the app could simply display red, yellow, and green lights to indicate the aircraft maintenance status of each flight, assisting users in deciding which flight to take.

The first step for the application is to collect all data, beginning with the manufacturer data. Manufacturers of aircraft can send all data related to that aircraft via a smart contract.

The aircraft manufacturing data can be structured within a blockchain and used by the airline company. Similarly, procurement data will be stored on the Blockchain.

Using procurement and manufacturing data, the airline company can easily create electronic flight logs or any other information logs required for any other system. In parallel, the flight logs and manufacturing and procurement data can be utilized through the smart contracts by MRO service providers to generate maintenance data. So at the first layer of the dApp architecture development, all types of maintenance data and support data are captured and gathered in the Blockchain.

The next step is to process the data after it has been captured and structured. Now that the data is in the Blockchain, the next architectural requirement is interfaced through which auditors, customers, or resale agencies can interact with the app and trust the data. Designing and developing of dApp interfaces is a multi-dimensional process. A lot of factors and attributes need to be factored in to design the interfaces of a dApp. The following section explains how the dApp interfaces are conceptualized and built, what factors are to be considered and how to bring up everything together.

For easy understanding, we will continue referring to the sample dApp- the aircraft maintenance record keeping application. As previously stated, the first layer of dApp architecture development is data capturing on the Blockchain. Referring back to the sample dApp discussed here, it can be developed in a couple of blockchain platforms. One possibility is a permissioned Blockchain, in which only the permissioned stakeholders capture and gather data.

Then there will be a public blockchain platform, such as XDC or Ethereum, where all public information will be stored in complete transparency for end-users to see.

Then, for data transfer, bridges could be built between the permissioned and public Blockchains. Now, the immediate question is which blockchain protocol to pick.

It can be decided based on 8 factors, viz:. The type: Whether you are building a private network or bringing your data to a public network. Speed: Do you want a real-time recording of transactions or scheduled recording, like once in a day, week, or month, as required. Bridging capacity: Do you want your network to talk to other protocols?

Do you want a hybrid environment? Cost: Another important factor is certainly the cost, and it includes storage cost on the network, execution cost, development cost, and all. Some of the major factors are:.

Regarding user identity, the first step is to determine whether to keep the identity centralized or decentralized. The identity of the user is an important factor in defining the user flow or interface. The following key points about user identity must be clearly defined: whether the user identity will be stored as a decentralized or centralized entity, where it will be saved, and what information it will contain.

In web 2, people sign up to log into systems and view data by using their Google, Facebook, or Twitter accounts, as well as their email addresses and phone numbers.

In web3, this logging happens through wallets. The user identity is hidden behind the wallet in this case, and the identity is not even on the network. So, whereas web 2 applications include identity as part of the data, the architecture for blockchain applications separates identity from data.

In most cases, identity is not linked to data at all in a pure on-chain application. Returning to the aircraft maintenance application. So, in this case, identity must be made public in order for it to be transparent. However, revealing the identity of a user who is searching for a flight from New York to San Francisco is meaningless. But again, when someone tries to buy a ticket, revealing the identity gets imperative.

Here, key considerations include where to save authorization and roles, regulating user movements, and ensuring that roles are properly managed. Users have control over their data in blockchain applications. Assume an employee is in possession of an enterprise data record. As a result, the application architecture design must consider what data is going on and off-chain. Certain blockchain platforms, such as Hyperledger, include authorizations and roles as part of their platform.

Notifications are mostly off-chain and send alerts about the actions happening on-chain and off-chain. There are various business logic layers in our sample application пїЅ flight maintenance record keeping. There is business logic for data acquisition to find data from various sources such as auditors, maintenance agencies MROs, etc.

Here the complex part of the decision tree is to decide whether to keep the business logic in the interfaces or into the smart contract.

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