The integration of renewable rnergy sources (RESs) into the power grid involves operational challenges due to the inherent RES energy-production variability. Imbalances between actual power generation and scheduled production can lead to grid instability and revenue loss for RES operators and aggregators. To address this risk, in this paper, we introduce a mutually beneficial bilateral trading scheme between a RES and a DR aggregator to internally offset real-time energy imbalances before resorting to the flexibility market. We consider that the DR aggregator manages the energy demand of users, characterized by uncertainty in their participation in DR events and thus the actual provision of flexibility, subject to their offered monetary incentives. Given that the RES aggregator faces penalties according to dual pricing for positive or negative imbalances, we develop an optimization framework to achieve the required flexibility while addressing the trade-off between maximizing the profit of the RES and DR aggregators and appropriately incentivizing the users. By using appropriate parameterization of the solution, the achievable revenue for the imbalance offsetting can be shared between the RES and the DR aggregators while keeping users satisfied. Our analysis highlights the interdependencies of the demand–production energy imbalance on user characteristics and the RES and DR aggregator profits. Based on our results, we show that a win–win outcome (for the RES and DR aggregators and the users) is possible for a wide range of cases, and we provide guidelines so that such bilateral agreements between RES and DR aggregators could emerge in practical settings.

Federations of Infrastructure Service Providers (InfSPs) has emerged as a practice to successfully serve demanding applications in cloud- and edge-computing environments, by overcoming the limitations of each such provider (in terms of available resources, geographic coverage etc.). In this paper, we develop innovative effective mechanisms and policies for the decentralized management of InfSP federations, considering the needs both for resource allocation meeting service composition requirements and for performing a fair and efficient distribution of profits. Resource allocation is performed by means of a greedy algorithm that includes an opportunistic and an adjustment phase. For determining the payments of participating InfSPs, we introduce an innovative sealed-bid reverse auction that combines VCG and first-price auction mechanisms; these are coupled with a sophisticated federation wallet management mechanism serving as a sink for the federation revenues. This hybrid mechanism possesses several nice properties including efficiency, long-term budget balance, truthfulness and individual rationality. Moreover, we present how our solution can be implemented in a decentralized, privacy-preserving and trustworthy manner over a blockchain, achieving bid privacy, non-repudiation and public verifiability. Our approach is evaluated by means of extensive experiments, the results of which reveal that resource allocation is either optimal or very close thereto, while individual InfSP profits as well as total federation profits are maximized. Moreover, the results confirm that the VCG mechanism alone cannot guarantee budget balance, thus justifying the necessity for our hybrid sophisticated solution.

Transacting entities online may still become victims of fraud, cyber-threats, low quality or performance, privacy loss, unfair pricing, biases in matching offers to requests, among others. Blockchain and other decentralized technologies may provide remedy towards trustworthy online transactions. This paper proposes a blockchain-based market framework that enables trustworthy transactions. We first define the functionalities that such a market framework should combine, namely mechanisms for service discovery, decentralized reputation, price determination, self-sovereign identities and verifiable credentials, fair exchanges, anonymity, asset digitization, cryptocurrencies, invoicing, and more. Then, we describe blockchain-based solutions for addressing each one of these functionalities. Finally, we exemplify the operation of the market in three real-world use cases.

Without a doubt the Internet of Things (IoT) paradigm has been gaining attention over the last years. With the deployment of low cost sensors, a plethora of information is made available, giving rise to intelligent systems that combine data from multiple sources. Multiple IoT platforms have been developed to support different application domains such as smart cities, health, industry 4.0, etc. However, the vertical focus and usually isolated development of such platforms pose difficulties in offering cross-domain smart applications to meet society's needs. To this end, interoperability frameworks have emerged to allow the interplay of different platforms as well as the formation of federations among the entities contributing IoT devices through such platforms. The decentralized nature of IoT data federations presents challenges when it comes to their management and governance, particularly in ensuring fairness, security, trustworthiness and transparency among its members. However, permissioned blockchain-based solutions hold significant potential in addressing these issues due to their inherent characteristics. In this work, we propose a blockchain solution based on the Hyperledger Fabric for the decentralized management of IoT federations and their gover-nance by utilizing voting-based configurable rules that abide to the concept of Decentralized Autonomous Organizations (DAOs). The solution includes smart contracts for the secure creation and management of federations exposed through APIs, as well as a voting application for enabling the DAO dynamic. Our solution demonstrates a secure, trustworthy and transparent way for the formation and membership control of IoT federations, that holds potential for extension with smart contracts related to data marketplace, as well as reputation and tokenization mechanisms.

In recent years, on the one hand, we have witnessed the rise of blockchain technology, which has led to better transparency, traceability, and therefore, trustworthy exchange of digital assets among different actors. On the other hand, achieving trustworthy content exchange has been one of the primary objectives of the Semantic Web, part of the World Wide Web Consortium. Semantic Web and blockchain technologies are the fundamental building blocks of Web3 (the third version of the Internet), which aims to link data through a decentralized approach. Blockchain provides a decentralized and secure framework for users to safeguard their data and take control over their data and Web3 experiences. However, developing trustworthy decentralized applications (Dapps) is a challenge because many blockchain-based functionalities must be developed from scratch, and combined with data semantics to open new innovative opportunities. In this survey paper, we explore the cross-cutting domain of the Semantic Web and blockchain and identify the critical building blocks required to achieve trust in the Next-Generation Internet. The application domains that could benefit from these technologies are also investigated. We developed a deep analysis of the published literature between 2015 and 2023. We performed our analysis in different digital libraries (e.g., Elsevier, IEEE, ACM), and as a result of our research, we retrieved 137 papers, of which 97 were retrieved as relevant to include in the paper. Furthermore, we studied several aspects (e.g., network type, transactions per second) of existing blockchain platforms. Semantic Web and blockchain technologies can be used to realize a verification and certification process for data quality. Examples of mechanisms to achieve this are the Decentralized Identities of the Semantic Web or the various blockchain consensus protocols that help achieve decentralization and realize democratic principles. Therefore, Semantic Web and blockchain technologies should be combined to achieve trust in the highly decentralized, semantically complex, and dynamic environments needed to build smart applications of the future.