Abstract
Social Internet of Things (SIoT) is an extension of the Internet of Things (IoT) that converges with social networking concepts to create social networks of interconnected smart objects. This convergence allows the enrichment of the two paradigms, resulting into new ecosystems. While IoT follows two interaction paradigms, human to human (H2H) and thing to thing (T2T), SIoT adds on human-to-thing (H2T) interactions. SIoT enables smart " social objects " that intelligently mimic the social behavior of human in the daily life. These social objects (SOs) are equipped with social functionalities capable of discovering other SOs in the surroundings and establishing social relationships. They crawl through the social network of objects for the sake of searching for services and information of interest. The notion of trust and trustworthiness in social communities formed in SIoT is still new and in an early stage of investigation. In this article, our contributions are threefold. First, we present the fundamentals of SIoT and trust concepts in SIoT, clarifying the similarities and differences between IoT and SIoT. Second, we categorize the trust management solutions proposed so far in the literature for SIoT over the last six years and provide a comprehensive review. We then perform a comparison of the state-of-the-art trust management schemes devised for SIoT by performing comparative analysis in terms of trust management process. Third, we identify and discuss the challenges and requirements in the emerging new wave of SIoT, and also highlight the challenges in developing trust and evaluating trustworthiness among the interacting SOs.