## 2 An Overview
### Blockchain, BIM and IoT  
Blockchain technology, born from the world of cryptocurrencies with Bitcoin, has started a real digital revolution that embraces numerous sectors from the banking and finance sector to insurance, from retail to agrifood, passing through the tracking of goods, and the public administration sector [8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. In particular, the implementation of the Blockchain in the public administration and business sectors would help citizens to have a secure and shared digital identity. It would allow us to solve some problems considered crucial in relations with public administrations and businesses, such as trust, transparency and security, and to implement the so-called Once Only Principle according to which citizens, institutions and companies must provide the authorities with certifications, attestations, declarations, or other documents once. Blockchain represents a great opportunity for the digitization of the public and private sectors as it not only reduces costs, waste of time and bureaucratic complexity, but also the distance between citizens, companies and institutions, strengthening trust in digital services and fostering their diffusion. All this means that public and private digital services must comply with the requirements of a model based on interoperability, must be inclusive and accessible in order to respond efficiently to the different needs of people and individual territories, and must be provided in a secure way guaranteeing the personal data protection. Looking at the public and private construction sectors, Blockchain technology, or distributed systems in general, offer a great potential when combined with innovative technologies such as BIM and IoT [21; 22; 23; 24] and could start a completely new era of collaboration. Today, on construction sites, communication in paper format is still very widespread and is strictly connected to evident inefficiencies and enormous costs. Consider, for example, that when the prospects of a given electrical or hydraulic system are printed, they could already be outdated due to changes that have become necessary during construction. Thanks to these technologies, it is possible to collect useful data to detect unexpected changes from what was designed, to detect delays in the execution of the project, to detect the causes of the delay that may be due to the failure to deliver the materials on time or to an incorrect order. Further, it is possible to collect data useful for detecting whether the work has been carried out through correct management between the various teams involved in compliance with the provisions of the project and therefore with what has been approved by the appropriate competent bodies. Concerning BIM, it is a methodology that uses a shared digital representation of a building to facilitate the design, construction, maintenance and in general the making of decisions regarding any aspect of its operating life [25; 26]. Therefore, BIM is essentially an IT methodology that can be used by insiders, professionals and, in theory, by any stakeholder linked to physical and non-physical design parts of a given building. It is a digital representation of all data relating to a building, such as geographic coordinates, floor plans, types and related properties of construction materials, the characteristics of individual systems, the chronology of the various construction, maintenance and demolition phases, and energy analysis. Thanks to BIM it is possible to know, in real time and unambiguously, for example the characteristics of the windows, or insulating materials used, or the performance of the air conditioning system installed, without the need to conduct a redundant inspection. The advantage is not of the individual designer, but of all those involved, such as builders, managers, property owners, public administrators and therefore of all stakeholders.