From Binary Trust to Graded Trust in Information Sources: A Logical Perspective

We present a concept of trust that integrates the truster's goal, the trustee's action that ensures the achievement of the truster's goal, and the trustee's ability and intention to do this action. This concept of trust is formalized in modal logic and is applied to the particular domain of trust in information sources. In this context trust may be derived, in particular, from the truster's belief's about some properties of the information source: validity, completeness, sincerity, competence, vigilance and cooperativity. In the last part of the paper we move beyond binary trust (i.e. either i trusts j or i does not trust j) in order to capture a concept of graded trust.