Trust on Information Sources: A Theoretical and Computational Approach

We start from the claim that trust in information sources is just a kind of social trust. We are interested in the fact that the relevance and the trustworthiness of the information acquired by an agent X from a given number of sources strictly depends and derives from the X's trust on each of these sources with respect the kind of that information. In this paper, we analyze the different dimensions of trust in information sources and formalize the degree of subjective certainty or strength of the X's belief P, considering three main factors: the X's trust about P just depending from the X's judgment of the source's competence and reliability; the sources' degree of certainty about P; and the X's degree of trust that P derives from that given source. Finally we present a computational approach based on fuzzy sets. I. DIMENSIONS OF TRUST IN INFORMATION SOURCES Which are the important specific dimensions of trust in information sources (TIS)? Many of these dimensions are quite sophisticated, given the importance of information for human activity and cooperation. We will simplify and put aside several of them. First of all, we have to trust (more or less) the source (F) as competent and reliable in that domain, in the domain of the specific information content. Am I waiting for some advice on train schedule? On weather forecast? On the program for the examination? On a cooking recipe? Is this F not only competent but also reliable (in general or specifically towards me)? Is F sincere and honest? Or leaning to lie and deceive? Will F do what has promised to do or "has" to do for his role? And so on. These competence and reliability evaluations can derive from different reasons, basically: a) Our previous direct experience with F (how F performed in the past interactions) on that specific information content , or better our "memory" about, and the adjustment that we have made of our evaluation of F in several interaction, and possible successes or failure relying on its information; b) Recommendations (other individuals Z reporting their direct experience and evaluation about F) or Reputation (the shared general opinion of others about F) on that specific information content; [3; 4; 5; 12; 13]; c) Categorization of F (it is assumed that a source can be categorized and that it is known this category), exploiting inference and reasoning:  inheritance from classes or groups were Z id belonging (as a good "exemplar");  analogy: Z is (as for that) like Y, Y is good for, then Z too is good for;  analogy on the task: Z is good/reliable for P he should be good also for P', since P and P' are very similar. (In any case: how much do I trust my reasoning ability? ). On this basis it is possible to establish the competence/reliability of F on the specific information content [2,6]. The two faces of F's trustworthiness (competence and reliability) are relatively independent 1 ; we will treat them as such. Moreover, we will simplify these complex components in just one quantitative fuzzy parameter: F's estimated trustworthiness; by combining competence and reliability. In particular we define the following fuzzy set: terrible, poor, mediocre, good, excellent (see figure 1) and apply it to each of the previous different dimensions (direct experience, recommendations and reputation, categorization). These competence and reliability evaluations can derive from different reasons, basically: Second, information sources have and give us a specific information that they know/believe; but believing something is not a yes/no status; we can be more or less convinced and sure (on the basis of our evidences, sources, reasoning). Thus a good source might inform us not only about P, but also about Actually they are not fully independent. For example, F might be tempted to lie to me if/when is not so competent or providing good products: he has more motives for fudging me. its degree of certainty about P, its trust in the truth of P. For example: "It is absolutely sure that P", "Probably P", "It is frequent that P", "It might be that P", and so on. Of course there are more sophisticated meta-trust dimensions like: how much am I sure, confident, in F's evaluation of the probability of the event or in his subjective certainty? 2 Is F not sincere? Or not so self-confident and good evaluator? For example, in drug leaflet they say that a given possible bad side effect is only in 1% of cases. Figure 1: Representation of the five fuzzy sets Have I to believe that? Or they are not reliable since they want to sell that drug? For the moment, we put aside that dimension of how much meta-trust we have in the provided degree of credibility. We will just combine the provided certainty of P with the reliability of F as source. It in fact makes a difference if an excellent or a mediocre F says that the degree of certainty of P is 70% (see §I.B). Third, especially for information sources it is very relevant the following form of trust: the trust we have that the information under analysis derives from that specific source, how much we are sure about that "transmission"; that is, that the communication has been correct and working (and complete); that there are no interferences and alterations, and I received and understood correctly; that the F is really that F (Identity). Otherwise I cannot apply the first factor: F's credibility. Let's simplify also these dimensions, and formalize just the degree of trust that F is F; that the F of that information (I have to decide whether believe or not) is actually F. In the WEB this is an imperative problem: the problem of the real identity of the F, and of the reliability of the signs of that identity, and of the communication. These dimensions of TIS are quite independent of each other (and we will treat them as such); we have just to combine them and provide the appropriate dynamics. For example, what happen if a given very reliable source F' says that "it is sure that P", but I'm not sure at all that the information really comes from F' and I cannot ascertain that? In a sense it is a transitivity principle [7]: X trust Y, and Y trust Z; will X trust Z? Only if X trusts Y "as a good evaluator of Z and of that domain". Analogously here: will X trust Y because Y trusts Y? Only if X trust Y "as a good and reliable evaluator" of it-self. A. Additional problems and dimensions We believe in a given datum on the basis of its origin, its source: perception? communication? inference? And so on. A) The more reliable (trusted) the F the stronger the trust in P, the strength of the Belief that P. This is why it is very important to have a "memory" of the sources of our beliefs. However, there is another fundamental principle of the degree of credibility of a given Belief (its trustworthiness): B) The many the converging sources, the stronger our belief (of course, if there are no correlations among