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ARSPA04Sadri, Toni1 A Logic-Based Approach to Reasoning with Beliefs about Trust ARSPA 2004 Fariba Sadri 1 and Francesca Toni 1,2 1: Department of Computing, Imperial College, UK 2: Dipartimento di Informatica, Universita di Pisa, Italy

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ARSPA04Sadri, Toni2 Main Features of Our Work Security via handling of trust Adopting an existing general-purpose, logic-based framework to model trust Using abductive logic programming both for knowledge representation and reasoning Allowing both static and dynamic knowledge about trust: the dynamic knowledge allows agents’ belief in trustworthiness of other agents to evolve through interactions with them Using beliefs about trust in communication and negotiation policies

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ARSPA04Sadri, Toni3 Abductive Logic Programs P is a logic program: set of rules of the form Head Body A is a set of abducible predicates: in agents’ case A can consist of Actions and Observations I is a set of integrity constraints: set of if- then rules of the form Conditions Conclusions

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ARSPA04Sadri, Toni4 Abductive Answers Given and a query Q an answer to Q is (E, ) such that: E A is a set of ground abducible atoms, and P E entails Q , and P E satisfies I

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ARSPA04Sadri, Toni5 Abductive Proof Procedures Defined to compute abductive answers for given queries Several have been proposed - we use CIFF: –Endriss, Mancarella, Sadri, Terreni, Toni, The CIFF proof procedure for abductive logic programming with constraints, Proc. Jelia 2004 –Endriss, Mancarella, Sadri, Terreni, Toni, Abductive logic programming with CIFF: implementation and applications, Proc. CILC 2004

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ARSPA04Sadri, Toni6 Example: (part of) KB of agent a P: have(R, T) initially(R), not [given_away(R,T1)), T1

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ARSPA04Sadri, Toni7 Example: Abductive answers observation Q: tell(b, a, “give me a camera”, 10) I triggered evaluated in P have(camera,10) abduced tell(a, b, “ok, I’ll give you a camera”, T'), T'<15

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ARSPA04Sadri, Toni8 Representing Trust Policies: Static Trust trust(maria, anna, T) trust(maria, dracula, T) T>6, T<24 trust(maria, john, T) false

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ARSPA04Sadri, Toni9 Representing Trust Policies: Dynamic Trust trust(maria, X,T) tell(X,maria,”ok, I’ll give you R by T1”,T'), do(X, deliver(R, maria, T2)), T2 T1

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ARSPA04Sadri, Toni10 Representing Trust Policies: Context Dependent Trust trust(maria,X,T,Task) expert(X, Task, T) trust(maria,X,T,Task) has_a_goal(X,G,T), helps(Task,G) trust(maria, X,T, Task) tell(Y, maria, recommended(X, Task), T1), T1 T, trust(maria,Y,T)

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ARSPA04Sadri, Toni11 Representing Trust Policies: Role-Based Trust trust(maria,X,T,advice(Issue)) authorised(X,give_advice(Issue),T) authorised(X,give_advice(booking(Hotel),T) receptionist(X,Hotel,T)

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ARSPA04Sadri, Toni12 Using Beliefs About Trust In private communication policies: Determining how to respond to queries/requests from other agents Deciding who to contact for one’s information or other resource needs Answering other agents’ queries about trust

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ARSPA04Sadri, Toni13 Example: Using Beliefs About Trust Request for resources over time windows: If you want the resource back give it to people you trust: tell(X, a, “give me R from T1 to T2”), T), have(R,T), not need(a,R,T1,T2), need(a,R,T3,T4), T3>T2, trust(a,X,T) tell(a, X, “ok, I’ll give you R from T1 to T2, but I want R back before T3”,T'), T'

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ARSPA04Sadri, Toni14 Further General Information Research developed within EU project SOCS : This model of trust could be employed directly by KGP agents: –Kakas, Mancarella, Sadri, Stathis, Toni, The KGP model of agency, ECAI 2004 –Stathis, Kakas, Lu, Demetriou, Endriss, Bracciali, PROSOCS: a platform for programming software agents in computational logic, Proc 4 th International Symposium “From agent theory to agent implementation”, 2004

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ARSPA04Sadri, Toni15 Future Work Resolving conflicting information Incorporating security Experimenting with scaled up, more realistic examples and scenarios

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