## 2 Background and Related Work
This work is focused on smart city applications and aims to address specific challenges such as integrating diverse data sources and incorporating geographical data. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Product** & **Key Features** & **Scope for Innovation** \\ \hline FIWARE-ORION [44] & Publish/Subscribe Context Broker, allows for real-time context data management, also supports NGSI (Next Generation Service Interfaces) & More robust support for diverse data models, improved scalability, and enhanced data transformation capabilities \\ \hline Linksmart [45] & Offers open-source tools for IoT, focus on semantic interoperability, provides features like service catalogue and distributed marketplace for data and services and user-friendly UI/UX enhancements, support for newer IoT protocols, built-in analytics tools & \\ \hline Microsoft Azure (IoT Hub) [43] & Supports bi-directional communication between IoT applications and the devices it manage, supports a wide array of SDKs, built-in device authentication & Enhanced AI and ML capabilities, better integration with non-Azure systems, more comprehensive device management tools \\ \hline OpenIoT [46] & Open-source, focuses on semantic interoperability for cloud-based IoT, offers utility-based sensing via virtual sensors & More user-friendly deployment options, enhanced real-time analytics, better security features. \\ \hline Symbius IoT [42] & Offers a unified middleware solution, supports compatibility with major sensor manufacturers, streamlined data accessibility, reduced deployment complexities & Expanding compatibility, enhancing security, and offering richer data insights \\ \hline IBM Watson IoT Platform [47] & Includes advanced AI capabilities for data analytics, anomaly detection, and predictive maintenance. Demonstrates high scalability, real-time data processing, easy integration with other products, and provides tools for data management. & AI capabilities can be enhanced to support automated decisionmaking. In addition to this, it can include enhanced support for blockchain and edge computing, with the addition of tools to facilitate development of custom solutions. \\ \hline Google Cloud IoT Core [48] & Fully managed service that is scalable and allows seamless data integration. Moreover, it also provides efficient data management and robust security features. & Discontinued in August 2023 due to non-technical reasons. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._A proof of concept is provided using air quality monitoring as a case study. This study is a significant step towards developing a generic and sustainable platform for IoT data management. Although no specific challenges have been identified by the study, the proposed platform uses MQTT, which has associated security and privacy challenges [54]. These challenges are particularly grave for healthcare applications, where identity and data protection are the highest priorities. Therefore, this paper proposes the use of a blockchain-based decentralised identity system that will facilitate the authentication of users and administrators. Blockchain's potential for securing IoT devices and their usage is widely recognised in both academia and industry. Therefore, it is viewed as a technology that is all set to revolutionise how IoT devices are administered, operated, and, most importantly, secured. Recent research [55] introduced BPIIoT, a decentralised peer-to-peer Industrial Internet of Things platform underpinned by blockchain. This platform facilitates direct communication between peers in a trustless network without necessitating a central intermediary. Another significant contribution [56] integrated permissioned blockchain mechanisms into a privacy-conscious IoT middleware. This middleware functions without any central authority and does not intrinsically trust the IoT platform. Despite significant advancements in both IoT and blockchain and the growing research on their integration into IoT middleware, a clear gap persists.