A Multi-level Blockchain Approach to System of Systems for Smart Cities Interoperability
Blockchain. Smart Cities. Scalability. System of Systems
Smart Cities currently utilize computational solutions to enhance their citizens' quality of life. However, these systems can be difficult to integrate as they are often isolated, heterogeneous, and maintained by distinct organizations at different activity levels. Several ways exist to integrate systems, such as ah hoc or using some frameworks (patterns, protocols, microservice, middleware). Depending on how this systems integration is carried out, it can be classified into different levels of interoperation, from Independent (level 0) to Unified (level 5), characterized by the full interoperation, emergence of new functionalities, and management of the execution of these functionalities by participating systems in almost real-time. However, few approaches entirely provide interoperability to share data and services emerging new functionalities. The main challenge is to share data reliably and securely without having a centralizing entity such as a trusted third party. And it becomes even more complicated in the context of smart cities due to the presence of personal data that demands more privacy. To overcome this challenge, a trusted decentralized controller entity based on a consensus mechanism among network participants can be achieved using Blockchain technology. As a first attempt at an integration solution, it used microservices to serve as a bridge between the system and the blockchain, but this presented severe limitations during ah hoc integration. The second alternative was to use a middleware platform with its communication protocols and data formats to facilitate integration between systems and blockchain, but the creation of new functionalities resulting from interoperation has not yet been addressed. Therefore, it was seen that using the concepts of a System of System (SoS) was necessary. The SoS concept is one way to promote full interoperability between systems. SoS is a collection of several isolated systems that act interoperably as part of a more extensive and intricate system, forming a cohesive and complex entity. Smart cities can benefit by using SoS to integrate services and develop new features. However, SoS has limitations, such as increased costs, limited collaboration, and mistrust of shared data and services. Therefore, this doctoral dissertation proposes an architecture to explore how Blockchain can be combined with System of Systems concepts to provide trusted interoperability between Smart Cities systems.