# Toward a Trust Evaluation Mechanism in the Social Internet of Things
## 2 Augmentation of Trust Concept in the SIoT
### Trust Concept Clarification  
Trust is a complicated concept which was originally used in many disciplines in human life. In the SIoT environment, trust interplays between social sciences and computer science influenced by both objective and subjective factors from both participators and contextual characteristics [12].  
The earliest variant of trust in computer science is system security and data security that cover concepts of hardware, software and communications. A system is trustworthy if it is secure and not compromised, meaning that it identifies people accessing the system and only allows authorized users; and the data security ensures that data is only accessed by those authorized users even in the presence of adversaries. More than three decades ago, [PERSON] mentioned trust in his Turing Award lecture when writing a Unix program to be free of Trojan horses [13]. Security gets further complex in networked worlds such as the Internet and the IoT due to the increasing participants to systems throughout the networks, resulting in introducing more threats, vulnerability and risks. System security and data security are also more complicated when privacy is taken into account. For example, personal data security could be ensured (in some degree) but providers can use the data for their own purposes or sell to a third-party. In this case, data security might be compromised if the data owner's intent for data usage is violated. One of the solutions is a trust-based access control mechanism for data sharing in the environment of Smart City that we have proposed in [14].  
An advanced variant of trust for a computer system is _dependability_ that is evolved from reliability, security and privacy considerations. Besides security and privacy, reliability is a factor showing whether a systems is going to perform properly. Thus, dependability is de facto property of a system representing ability of the system to deliver secure and quality services by characterizing the security, privacy and reliability schemes in terms of some attributes such as availability, safety, integrity, confidentiality and reliability. [PERSON] and [PERSON] have defined this variant of trust as _\"infrastructure trust\"_[15]. In our perspective, dependability is one of the most important indicator in evaluating trustee' trustworthiness (in case the trustee is a computer system). The key distinction between trust and dependability is due to the enrolment of social interactions (of both humans and devices), which is modulated in form of social capital factors (Figure 0(a)). The social capital can interpret various aspects of individuals and social networks including behaviors, norms and patterns that have built up through social interactions over time that also help to reckon trust. In this regard, trust is an umbrella concept of dependability.  
Trust is originally a foundational aspect of human social relations; and when applying trust to the SIoT environment, it should be considered under a perspective of a trustor in correlation with a society. Social interactions, subjective viewpoint of individual entity, and environments should not be neglected [16]. We have pointed out that besides trustworthiness of a trustee, trustor's propensity and environmental factors such as vulnerabilities, threats and risks also contributes to the trust evaluation (Figure 1b). This is obvious because trust only occurs risky scenarios in which the trustor is going to be under vulnerability.