In recent years, blockchain technology has seen significant practical growth, yet it has not seen the same advancement from a theoretical perspective. This has led to the creation of numerous blockchains that are very different from each other and behave like isolated worlds. The research and development of theoretical frameworks, which define the fundamental properties of blockchains and define standards to follow for a more homogeneous implementation approach, have become extremely important. A theoretical model can help not only to design blockchains in the future but also to define a set of minimum requirements to be met for the creation of interoperability protocols between existing blockchains. In this work, we propose a theoretical model of blockchain that describes its most significant properties. Starting from our theoretical model, we present Smart Listeners , a blockchain interoperability protocol that finalises an inter-chain transaction with just two transactions: one on the source blockchain and one on the destination blockchain. The protocol is optimistic since changes on the source blockchain occur as if inter-chain transactions were successful. It is hybrid since it combines some properties of watchtowers and oracles in the off-chain components. We provide a benchmark on the performance of the proposed protocol in terms of latency and transactions per second. Finally, we define the minimum requirements that a blockchain should satisfy to allow the application of general-purpose interoperability protocols.

This article focuses on the concept of blockchain soulbound tokens, their potential applications, and their implementation in Ethereum-based blockchains. Soulbound tokens add an important piece to blockchain technology, as they could be the key to building Web3 and a trustworthy decentralized society. Issued and strictly linked to an account, representing the soul of a user, the soulbound token makes it possible to represent a property that only the user can have and that cannot be transferred, but only removed, which enhances security. To evaluate their impact on blockchain development, we first examine the concept of soulbound tokens, their potential applications, and their effective adoption. The application sectors include the creation of digital identity certificates, ownership certificates, reputational certificates, governance, and the healthcare sector. We then report and describe relevant blockchain token standards, including soulbound token standards, provided in the form of Ethereum Improvement Proposals. Finally, to study the efficacy of the implementation of soulbound tokens, we propose a case study that includes the design and development of a decentralized vaccine certification prototype based on soulbound tokens. In our system, the vaccination data produced by the health authority is fully decentralized and implemented as the issuance of soulbound tokens for the benefit of a citizen’s soul account. As a result, the citizen is the only owner of the vaccination data.

Smart contracts have played a pivotal role in the evolution of blockchains and Decentralized Applications (DApps). As DApps continue to gain widespread adoption, multiple smart contract languages have been and are being made available to developers, each with its distinctive features, strengths, and weaknesses. In this paper, we examine the smart contract languages used in major blockchain platforms, with the goal of providing a comprehensive assessment of their main properties. Our analysis targets the programming languages rather than the underlying architecture: as a result, while we do consider the interplay between language design and blockchain model, our main focus remains on language-specific features such as usability, programming style, safety and security. To conduct our assessment, we propose an original benchmark which encompasses a wide, yet manageable, spectrum of key use cases that cut across all the smart contract languages under examination. • We give an abstract overview of smart contract platforms, discussing the impact of different design choices. • We illustrate by examples how different design choices give rise to different programming styles for smart contracts. • We consider 6 leading smart contract languages: Solidity (Ethereum), Rust (Solana), Aiken (Cardano), PyTeal (Algorand), Move (Aptos), SmartPy (Tezos). • We develop an open-source benchmark of use cases of smart contracts, implemented in all the languages in our selection. • Based on our benchmark, we evaluate smart contract languages focussing on their security, code readability, usability, and functionalities.

The use of blockchain oracles is becoming increasingly widespread as it responds to the problem of providing the blockchain with external data automatically. In this paper, we focus on the use of blockchain oracles for the certification of articulated data. In particular, we show how it is possible to design and implement a DApp capable of providing documents on request without these data permanently residing on the blockchain. We present a case study of the on-demand provision of university curriculum, fully managed via a blockchain oracle. In this system, the smart contract will not record data permanently but only for the time necessary for its use. The system is intended to allow a user to request and obtain data only about herself. The paper also presents a classification of the types of blockchain oracles and their most common applications. The case study will be presented as blockchain-oriented software, and in terms of architecture and dynamics using UML diagrams, the benefits and drawbacks of the approach are discussed.

We discuss the contribution of the Petri net formalism to the BOSE for Smart Contract design and development. We address this discussion based on the analysis of recently published literature works we obtained by querying Scopus and Google Scholar. Different types of Petri nets, including coloured Petri nets and workflow nets, and different types of tools emerge from our analysis. Our discussion includes the classification into three categories of application of the Petri net formalism in the design and development of Smart Contracts, namely modeling, generation, and verification.

This paper presents a first investigation to join agile blockchain-oriented software development principles with sustainability software design principles. The development of blockchain-oriented software should always be performed in the awareness of the potential effects generated from its use, especially in a long-term life cycle perspective. In other terms in the awareness of its present and future sustainability. By using the principles of sustainability software design and recognized the role of blockchain-oriented Agile methodologies to manage changes in technology and requirements, we present a new Agile method for the development of blockchain-oriented systems that includes sustainability awareness practices within the development phases, in particular in the requirements and the acceptance tests. This allows to deal with blockchain-oriented systems sustainability immediately and during the incremental and iterative development process. The paper describes the process in its phases and provides an example of an application to the supply chain sector.

Summary This article proposes a blockchain oriented platform to guarantee the origin and provenance of food items in a Smart Tourism Region context. Local food and beverage, in fact, can become a good combination to attract tourist and to promote the area provided that their provenance is clearly certified. We designed and developed a blockchain‐based system to manage an agri‐food supply chain for tracking food items. By using smart contracts the platform guarantees transparency, efficiency and trustworthiness. Our system is particularly suitable to manage cold chain since the system interfaces with IoT network devices providing detailed information about data monitoring food such as storage temperature, environment humidity, and GPS data. All involved actors can share data and information in a more efficient, transparent, and tamper proof way than traditional systems. The final consumer can access with transparency to all the agri‐food chain of the purchased product and verify provenance by retrieving all detailed information registered in the blockchain public ledger. The proposed system has been designed according to the ABCDE method, an agile development process recently conceived, to obtain a higher software quality to design a general blockchain system by means software engineering practices. A real case study applied to local products from Sardinia, Italy, is proposed at the end of the article.

Abstract An Initial Coin Offering (ICO) is an innovative way to raise funds and launch a startup. It is also an opportunity to take part in a project, or in a DAO (Decentralized Autonomous Organization). The use of ICO is a global phenomenon that involves many nations and several business categories: ICOs collected over 5.2 billion dollars only in 2017. The success of an ICO is based on the credibility and innovativeness of project proposals. This fund-raising tool contains however some critical issues, such as the use of tokens that have no intrinsic value and do not generate direct liquidity, and the role of investors in the management of the startup. We analyzed if the Lean Startup methodology is helpful to face this critical aspects and we examined some ICOs in which the proposing team states explicitly that a lean startup approach is used.

A Blockchain is a global shared infrastructure where cryptocurrency transactions among addresses are recorded, validated and made publicly available in a peer-to-peer network. To date, the best known and important cryptocurrency is the bitcoin. In this paper, we focus on this cryptocurrency and in particular on the modeling of the Bitcoin Blockchain by using the Petri Nets formalism. The proposed model allows us to quickly collect information about identities owning Bitcoin addresses and to recover measures and statistics on the Bitcoin network. By exploiting algebraic formalism, we reconstructed an Entities network associated to Blockchain transactions gathering together Bitcoin addresses into the single entity holding permits to manage Bitcoins held by those addresses. The model allows also to identify a set of behaviors typical of Bitcoin owners, like that of using an address only once, and to reconstruct chains for this behavior together with the rate of firing. Our model is highly flexible and can easily be adapted to include different features of the Bitcoin cryptocurrency system. By exploiting algebraic formalism, we reconstructed an Entities network associated to Blockchain transactions gathering together Bitcoin addresses into the single entity holding permits to manage Bitcoins held by those addresses. The model allows also to identify a set of behaviors typical of Bitcoin owners, like that of using an address only once, and to reconstruct chains for this behavior together with the rate of firing. Our model is highly flexible and can easily be adapted to include different features of the Bitcoin cryptocurrency system.

Teledermatology offers the possibility of improving access to dermatologic care by using telecommunication technologies for connecting several medical centers and enabling to exchange information about skin conditions over a distance. This paper describes the main points of the implementation of a teledermatology project following the so-called smart region paradigm. A case study is presented to describe how the implementation of a virtual organization model using teledermatology is able to promote and facilitate the diagnosis on skin diseases and improve the quality of care for rural and remote areas. Initial results and assessment by general practitioners and dermatologists show that the proposed software platform can be used as a decision support system for dermatological patients.