This paper presents a decentralized Web-based architecture designed to support the development of distributed, dynamic, context-aware and interoperable services and applications. The architecture enables the detection and notification of changes over the Web of Data by means of a content-based publish-subscribe mechanism where the W3C SPARQL 1.1 Update and Query languages are fully supported and used respectively by publishers and subscribers. The architecture is built on top of the W3C SPARQL 1.1 Protocol and introduces the SPARQL 1.1 Secure Event protocol and the SPARQL 1.1 Subscribe Language as a means for conveying and expressing subscription requests and notifications. The reference implementation of the architecture offers to developers a design pattern for a modular, scalable and effective application development.

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This work describes a network of low power/low-cost microelectromechanical-(MEMS-) based three-axial acceleration sensors with local data processing and data-to-cloud capabilities. In particular, the developed sensor nodes are capable to acquire acceleration time series and extract their frequency spectrum peaks, which are autonomously sent through an ad hoc developed gateway device to an online database using a dedicated transfer protocol. The developed network minimizes the power consumption to monitor remotely and in real time the acceleration spectra peaks at each sensor node. An experimental setup in which a network of 5 sensor nodes is used to monitor a simply supported steel beam in free vibration conditions is considered to test the performance of the implemented circuitry. The total weight and energy consumption of the entire network are, respectively, less than 50 g and 300 mW in continuous monitoring conditions. Results show a very good agreement between the measured natural vibration frequencies of the beam and the theoretical values estimated according to the classical closed formula. As such, the proposed monitoring network can be considered ideal for the SHM of civil structures like long-span bridges.

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In the next few years, the W3C Web of Things (WoT) platform will represent a reference solution toward the deployment of fully interoperable systems, hence unlocking the potential of the IoT paradigm on several use-cases characterized by the current fragmentation of devices and technologies. At the same time, the worlwide adoption of the W3C WoT architecture depends on many factors, including also the availability of support tools that might facilitate the deployment of novel WoT applications or the integration with traditional IoT systems. To this purpose, the paper presents the WoT Store, a complete software platform enabling the discovery and management of W3C Things, the monitoring of its properties and events, and the invoking of actions, all within the same dashboard. In addition, the platform leverages on the semantic description of each Thing with the goal of easing and automatizing the installation and execution of WoT applications, e.g. defining the behaviour of a Thing or implementing mash-up operations from multiple Things. We sketch the main features, the architecture and the prototypal implementation of the WoT Store. Moreover, we discuss the WoT Store capabilities on three IoT use-cases, i.e. industry 4.0, smart agriculture and home automation. I. CONTEXTSince the beginning, the Internet of Things (IoT) suffered from lacks of common interaction and communication paradigms that translated into the creation of several, independent technology silos, with severe concerns on the deployment of heterogeneous systems. The interoperability can be considered both a challenge and a market opportunity: according to [1], almost 40% of the value of IoT markets can be unlocked when achieving full interoperability among heterogeneous IoT systems. Among the several research projects and standardization initiatives proposed so far and addressing the IoT interoperability issue, a key role is played by the World Wide Web Consortium (W3C), i.e. the leader of Open Web platforms, and more specifically by the Web of Things (WoT) working group [2]; this latter has been/is working on the proposal of a platform-independent API and of service discovery mechanisms for the full IoT interoperability. Clearly, a worldwide acceptance of the W3C WoT platform is fundamental for the purpose of mitigating the fragmentation of WoT-related initiatives, and of the definition of a reference solution; on the opposite, there is always the risk of a new IoT technology silo. To this purpose, it is worth remarking that the software acceptance in industrial scenarios is largely influenced by the size and the quality of its Software Ecosystem (SECO). This latter can be defined as the set of software solutions that enable, support, and automatize the activities and transactions by the actors in an associated social or business scenario. As reported in [3], several studies in the literature investigate the success of a software solution and its SECO as vehicle to attract new players. The availability of supporting software modules is acknowledged ...