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

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

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

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

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

ARSPA04Sadri, Toni6 Example: (part of) KB of agent a P: have(R, T)  initially(R), not [given_away(R,T1)), T1<T] have(R, T)  obtained(R,T2), T2<T, not [given_away(R,T1)), T2<T1<T] + auxiliary definitions for given_away and obtained I: tell(X, a, “give me R”, T), have(R,T)  tell(a, X, “ok, I’ll give you R”,T'), T'<T+5 A: tell(a,X,S,T), tell(X,a,S,T)

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

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

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<T trust(maria, X, T)  friend(maria,X,T), honest(X,T) friend(maria,X,T)  do(X,lend_money(maria), T'), T'<T honest(X,T), in_prison(X,T'), T'  T  false

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)

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)

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

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'<T+5

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

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