  A social approach can be exploited for the Internet of Things (IoT) to manage
a large number of connected objects. These objects operate as autonomous agents
to request and provide information and services to users. Establishing
trustworthy relationships among the objects greatly improves the effectiveness
of node interaction in the social IoT and helps nodes overcome perceptions of
uncertainty and risk. However, there are limitations in the existing trust
models. In this paper, a comprehensive model of trust is proposed that is
tailored to the social IoT. The model includes ingredients such as trustor,
trustee, goal, trustworthiness evaluation, decision, action, result, and
context. Building on this trust model, we clarify the concept of trust in the
social IoT in five aspects such as (1) mutuality of trustor and trustee, (2)
inferential transfer of trust, (3) transitivity of trust, (4) trustworthiness
update, and (5) trustworthiness affected by dynamic environment. With network
connectivities that are from real-world social networks, a series of
simulations are conducted to evaluate the performance of the social IoT
operated with the proposed trust model. An experimental IoT network is used to
further validate the proposed trust model.
