# IoT-Enabled Smart Cities: A Review of Concepts, Frameworks and Key Technologies
## 4 Discussion on Recent Trends, Open Challenges and Future Directions
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Smart City Domains** & \multicolumn{3}{c}{**Services, Applications**} & \multicolumn{2}{c}{**IoT and Sensing**} & \multicolumn{2}{c}{**Real-World Cases**} \\  & & **and Features** & & **Technologies Involved** & **Real-World Cases** \\ \hline Smart Industry & - & Industry 4.0 & & & & \\ Smart Industry & - & Smart manufacturing & - & Cyber-physical systems (CPS) & - & Dublin [90] \\ and Production & - & Predictive maintenance & - & Cloud-based manufacturing [87] & - & Shenzen [3] \\  & - & Smart agriculture & & & & \\  & and farming & & & & & \\ \hline Smart Energy & - & Energy management & - & Tribeelectric nanogenerators & - & Nice [58] \\  & - & Sustainable energy & & (TENG) and electrostatic energy & - & Padova [96] \\  & - & harvesting & & harvesters (EEH) [59] & - & Atlanta [3] \\  & - & Smart lighting & - & Light luminosity sensors [94] & - & Helsinki [97] \\  & - & Smart grids & - & Energy consumption measuring & - & Masdar City [98] \\  & - & & devices [95] & & - & Singapore [102] \\  & - & Air quality monitoring & & & - & Amsterdam [103] \\ Smart Environment & - & Weather monitoring & - & Ambient sensors [7] & - & Stockholm [66] \\  & - & Smart waste management & - & Big data from satellite, LiDAR & - & Busan [3] \\  & - & Smart water & & and GIS data [99] & - & Florence, Pisa, Livorno \\  & - & Smart water & & & & and Modena, Santiago de \\  & & & & & & Composeta and \\  & & & & & Zaragoza [104] \\ \hline Smart Healthcare & - & Telemedicine & - & Wearable or implanted devices & & \\  & - & Remote patient monitoring & & for remote patient monitoring & & \\  & (RPM) and healthcare & & (RPM) [20] & - & Singapore [3] \\  & & tracking & - & Body sensor networks (BSNs) & - & Stockholm [110] \\  & - & Smart hospitals & & and wireless body area networks & - & Hefei [111] \\  & - & e-health records & & (WBANs) [105] & - & Helsinki [112] \\  & - & management & - & Standards for information & \\  & - & Disease prediction and & & management (HL7, & & \\  & prevention & & PACS-DICOM, etc.) [107] & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._imply important social involvement, for instance, in security and resilience, since they allow the building of more resilient tools that are able to perform real-time analysis and simulations, e.g., those used by local public authorities for early warnings and alerts in critical events, such as disaster management [99] and resilience planning. Moreover, many IoT solutions are still oriented toward traditional programming environments, while the most recent trends show an advancement in the exploitation of visual paradigm languages (VPL) [15; 32], including Node-RED, for implementing workflows for IoT applications. The adoption of microservice-oriented architectures leads toward the overcoming of the monolithic platform approach [3] since the microservice paradigm allows the reuse of software components and blocks. Moreover, microservice architectures are open to extensions and they can also exploit external services more easily (when necessary for delegating part of the computation as well as accessing additional services or applications) [29]. For instance, they can be easily adapted to support almost all kinds of IoT and communication protocols and also support data-driven and event-driven push modalities. This is moving in the direction of the implementation of smarter frameworks for business intelligence and data analytics, as well as more interactive visual analysis tools [32]. This deeper level of integration and complexity of IoT-enabled smart city platforms should bring advancements in performing real-time simulations, what-if analysis and supporting decision-making processes, which is the basis of the production of smarter and more efficient services and applications for all involved stakeholders. Furthermore, IoT-enabled smart city platforms are evolving toward cross-organization and multitenancy IoT platforms and applications.