# CATSWoTS: Context Aware Trustworthy Social Web of Things System
## 2 Background Study
### Trust Management Systems  
IoT is a network of interconnected objects and humans as well. The entities can work without the intervention of humans [10]. The presence of IoT devices around humans creates opportunities for malicious activities. Hence, it makes the selection of services among the pool of services a tedious task. Furthermore, access to the data acquired by these entities must ensure the secrecy and privacy of data by emphasizing reputation and trust [13]. A classification tree for trust composition is developed byGuo et al. [14]. In this survey, five design dimensions were identified. The authors describe that, in state-of-the-art approaches, these five dimensions are considered necessary for a trust computation model. It is recognized that the researchers follow one of the sub-dimensions of these five dimensions. Trust composition needs to consider QoS such as reliability, competence, and social relations. Trust evidence needs to be broadcast to peers. It can be done through distributed and centralized approaches. For aggregating trust pieces of evidence, various techniques are identified in this survey which are the weighted sum, belief theory, Bayesian inference, fuzzy logic, and regression analysis. For updating trust, event-driven or time-driven approaches are used. Similarly, single or multi-trust are used for trust formation [14]. A comprehensive review of the state of the art related to IoT architectures, Privacy Enhancing Technologies (PETs), and privacy laws was carried out in [15]. It was identified that implementing PETs at various layers of IoT architecture could ensure the privacy needs. The study elaborated the principles of privacy legislation which were linked with PETs. It was identified that eight basic principles laid the foundation of European privacy laws [15]. Moreover, it was assessed that careful deliberation is required for the usage of PETs. [PERSON] et al. [16] presented a system for resolving the issue of security and privacy. Different levels were introduced for exchange which was done through a contract. These levels were applied to establish trust between devices and which then monitored and controlled IoT devices. For this, identification and monitoring of devices and connection protocols were suggested. The drawback of this research was that it focused on the privacy and security of data, but the context while trusting on the devices and the trust based on the quality of services were ignored [16]. A trust management protocol [17] was proposed which changed dynamically in IoT. Scalability, adaptability, survivability and the quality at service level were not focused. In another research, [PERSON] et al. proposed a system which focused on data integrity, privacy, and availability [18]. However, trustworthiness in terms of quality of service was not given attention in this research. [PERSON] et al. [19] focused on managing the authentication, authorization, interoperability, and business model. The challenges faced by distributed computing were focused on this research; however, context-awareness was not given attention in this research. A research work focusing on integrity and confidentiality of real-time IoT systems was done by [PERSON] et al. [20]. A hybrid architecture called DARE based on wireless sensor network and mesh networking was proposed. In [21], an approach for QoS based service selection was proposed. It also considered utility function and distance estimation for the service recommendation in addition to QoS attributes. Pearson Correlation Coefficient (PCC) and the Haversine distance formula were used to improve the performance level. Service categorization was carried out based on distance, PCC, and utility function in order to select the best suitable service. The proposed work only helped in identifying the location and QoS based services and did not consider context related attributes such as capacity and time. In addition, history of service providers considered just for the utility function.