# Predicting Reputation in the Sharing Economy with Twitter Social Data
## 2 Background  
### Trust and Reputation Notions and Computational Models  
Trust and reputation play an important role in human society. Thus, they have become subject of study of a wide array of disciplines, including sociology [17; 18], social psychology [17; 19], anthropology [20], political science [21], philosophy [22; 23], law [24], economics [25], and computer science [26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36]. Several factors in today's society make the concept of trust more relevant [37]. Contemporary society has become more interdependent because of the globalization process. In addition, people have more available options in all domains of life, which makes both our decisions and those of others less predictable. Moreover, organizations have become more opaque and complex. Another source of unpredictability is the increasing dependence on technology, which brings new threats and vulnerabilities. Trust and trustworthiness is our strategy to deal with uncertain and uncontrollable future situations. As defined by [PERSON], \"Trust is a bet about the future contingent actions of others\" [37]. In this regard, [PERSON] [38] treats trust as a form of social intelligence that allows people to assess the degree of risks they face in social situations. Granting trust to a target is the result of the estimation of its trustworthiness, which can be determine using three main mechanisms [37]: reputation, performance, and appearance. Reputation is \"a record of past deeds\" [37]. Let's say we are evaluating how trustworthy an Uber driver is. The reputation would be based on the driver's rating. Performance refers to the present behavior. In the previous example, we would focus on how the driver is currently driving and maybe her conversation. Finally, appearance consists of superficial external signs relevant for trust, such as, for example, the driver's photo [39] or if the car is in good condition. Online transactions challenge our traditional mechanisms for evaluating trustworthiness since we cannot see and try the products or the providers. In addition, reputation rating could be dishonest or biased towards positive feedback [40]. Therefore, trust and reputation systems have tried to provide adequate substitutes for the traditional signs we use in the physical world and take advantage of Information and Communications technology (ICT) technologies for collecting this information and providing useful trust and reputation metrics [32]. Trust and reputation have a rich research tradition in Computer Science. Several surveys have provided an excellent overview of its representation, computational models, and applications in Web services [28], the Semantic Web [29], web sciences [41], Multi-agent systems [27; 31; 42], online service provision [34; 36; 32], Peer to Peer (P2P) applications [26], ad hoc networks [30; 33], and social networks [35]. The main mechanisms for managing trust are [26; 43]: (i) _policy-based trust_ that rely on security mechanisms such as credentials and access policies to grant access rights; and (ii) _reputation-based trust_, where past interactions are used for predicting future behavior; and (iii) _social network-based trust_ that also use social relationships between peers to compute trust. Policy-based trust relies on a trusted third party that serves as an authority for providing and verifying credentials. Policies can be expressed in policy specification languages [44]. Trust negotiation mechanisms enable building trust through a bilateral exchange of credentials preserving privacy [45]. Reputation-based trust systems should provide mechanisms for storing past experiences and calculating trust score. There are two main architectural types, centralized and distributed systems [32]. In centralized reputation systems, a central authority, the so-called reputation center, collects all the ratings and computes a public reputation score for every user.