# Toward a Trust Evaluation Mechanism in the Social Internet of Things  
[PERSON]  
1 Department of Computer Science, Liverpool John Moores University, Liverpool L3 3 AF, UK; [EMAIL_ADDRESS] (N.B.T. ); [EMAIL_ADDRESS] (B.A. )1 Department of Computer Science, Liverpool John Moores University, Liverpool L3 3 AF, UK; [EMAIL_ADDRESS] (N.  
human centric and holistic view of computing by analyzing observations, knowledge, and experiences from physical, cyber, and social worlds\" [2]. In the early years, most of IoT-related research articles have concentrated on RFID and Wireless Sensor Networks (WSNs) that aim at building underlying networking protocols, hardware and software components in order to enable interactions and communications among physical objects and cyber-space. However, a human-centric IoT environment in which human plays an important role in supporting application and services, are more and more perceptible. This is proven by the high rate of utilization of social phenomena and crowd intelligence when developing real-world IoT services. Consequently, the so-called Social Internet of Things (SIoT) has recently been proposed for illustrating the CPSS concept in which people are envisaged as an integral part of the IoT ecosystem [3; 4]. However, the merging of physical objects, cyber components and humans in the SIoT will introduce new concerns for risks, privacy and security. Consequently, managing risk and securing the SIoT are broad in scope and pose greater challenges than the traditional privacy and security triad of integrity, confidentiality, and availability [5]. In this regard, trust is recognized as an important role in supporting both humans and services to overcome the perception of uncertainty and risk when making a decision. Trust is a multifaceted concept used in many disciplines in human life influenced by both participators and environmental factors. It is an underlying psychological measurement to help a trustor to come up with a decision whether it should put itself into a risky situation in case a trustee turns out to be misplaced. As the aim of any SIoT services is to autonomously make decisions without human intervention, trust has been highlighted as a vital factor for establishing seamless connectivity, secure systems and reliable services. A trust platform could minimize the unexpected risks and maximize the predictability, which helps both SIoT infrastructures and services to operate in a controlled manner and to avoid unpredicted conditions and service failures. As the importance of trust in SIoT, recently, a large number of research groups have been intensively working on trust-related areas in various networking environments such as peer-to-peer (P2P) networks, wireless sensor networks, social networks, and the IoT; varying in many applications and services from access control [6] to e-Commerce [7; 8]. To develop a complete trust platform, various trust-related areas are necessarily taken into considerations such as trust evaluation and trust management [9]. In this article, we mainly focus on developing a trust evaluation model. Besides, researchers have also focused on developing trust management mechanisms dealing with trust establishment, dissemination, update and maintenance processes. Some articles have been proposed trust evaluation models based on a set of information (so-called _direct trust_) by extracting trustee's characteristics or by observing trustee's behaviors. This information are used to describe some trust-related characteristics of an entity that are coined as Trustworthiness Attributes (TAs); these TAs are combined to a final value for representing the trustee's trustworthiness. The trustworthiness is then unconsciously used as trust. Other approaches have measured trust based on third-party information about a trustee that the third-parties have been already interacted with, thus, they already gained some clues of trust (so-called _indirect trust_).