Argumentation and Trust: Issues and New Challenges Jamal Bentahar Concordia University (Montreal, Canada) University of Namur, Belgium, June 26, 2007

2 Overview Problem and Motivations Negotiation Framework Trustworthiness Model Implementation Application Areas

3 Context and Problem Multi-agent Systems: interacting autonomous agents Communication Protocols: specifying allowed communicative acts Open and dynamic MAS need flexible protocols Examples: negotiation, deliberation, and persuasion Security engineering: a new challenge in agent-based software engineering Distributed setting: e.g. semantic-grid computing Computational efficiency

4 Proposed Approaches for Interacting Agents Mental Approach Private states: Beliefs, Desires, Intentions, etc. Social Approach Public states: Social commitments Argumentative Approach Argumentation theory + reasoning Allen and Perrault, 1980 Cohen and Levesque, 1990 and others Singh, 2000 Colombetti, 2000 and others Amgoud and Maudet, 1999 McBurney et al., 2002 and others

5 Motivations How to trust negotiating agents within a multi-agent system: Resources sharing and mutual access Centralized Approaches Vulnerable to attacks Reasoning Capabilities Quantitative Probabilistic-based Decentralized Approach

6 Overview Problem and Motivations Negotiation Framework Trustworthiness Model Implementation Application Areas

7 Agent Architecture

8 Negotiation Framework Agent 1 Agent 2 Social Commitments + Argumentation Speech Act Theory + Action Logic Negotiation Specification Reasoning + Semantics

9 Negotiation Framework Argumentation Theory Agent Negotiation Support FlexibilityEfficiency Dialogue Games Relevance Theory Logic- based Reasoning

10 Dialogue Games Abstract structures that can be composed: Sequencing: Embedding: Parallelization: Argumentation-driven decision making process Game 1 Game 2, Game1 Game 2 …… Game 1 Game 2 //

11 Dialogue Games: Specification Initiative / reactive dialogue games A simple language Cond: generating arguments from the agent’s argumentation system Action_Ag 1 Action_Ag 2 Cond

12 Dialogue Games: Specification

13 Agent Communication Action_Ag i  {Make-Offer, Make-Counter- Offer, Withdraw, Satisfy, Violate, Accept, Refuse, challenge, Justify, Defend, Attack} Argumentation system Communicative Actions Supports

14 A powerful framework for interacting agents: Making decisions Assessing the validity of information Resolving differences of opinion Argumentation focuses on interactions where parties plead for and against some conclusion Essential ingredient of negotiation, persuasion and collaborative decision-making. Argumentation

15 The notion of argument: a pair An argument is a pair (P, c) where P is a set of beliefs and c is a formula, such that: i) P is consistent, ii) P c et iii) P is minimal Formal Argumentation

16 Attack relation: binary relation between arguments An argument (P 1, c 1 ) attacks another argument (P 2, c 2 ) iff c 1 c 2 or x P 2 | c 1 x Argumentation Dynamics

17 Argumentation Dynamics

18 Overview Problem and Motivations Negotiation Framework Trustworthiness Model Implementation Application Areas

19 Trust in MAS Two approach types into trusting multi-agent systems: centralized and decentralized Centralized approaches: e.g. eBay and Amazon Auctions The ratings are stored centrally and summed up to give an overall rating Reputation is a global single value The model can be unreliable, particularly when some buyers do not return ratings These models are not suitable for applications in open MAS such as agent negotiation

20 Trust in MAS Three main decentralized approaches: Building on agents’ direct experiences of interaction partners Using information provided by other agents Certified information provided by referees Examples: Regret, Referral, Fire

21 Qualitative approach: Using argumentation to reason about trust Quantitative approach: Probability function Rep : A  A  D  [0, 1] Local beliefs Global beliefs: testimonies of witnesses Foundation

22 Illustration

23 Central Limit Theorem and the Law of Large Numbers If M > w Then Return True Else Return False Assessing Agent’s Reputation

24 Timely Relevance Function

25 Reputation Graph Algorithm 1: Graph Construction

26 Algorithm2: Node Evaluation

27 Complexity Construction of the trust graph with n nodes and a edges n recursive calls of the function Evaluate-Node (Ag y ) Each node is visited once: Assessing the weight of a node Using the weight of its neighbors and input edges: Run time of the reputation algorithm:

28 Overview Problem and Motivations Negotiation Framework Trustworthiness Model Implementation Application Areas

29 System Architecture The system is designed as a society of interacting agents Agents are equipped with knowledge bases and argumentation systems Knowledge bases contain propositional formulae and arguments Platform: Jack Intelligent Agents + Java

30 System Architecture

31 Architecture of Negotiating Agent

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34 Overview Problem and Motivations Negotiation Framework Trustworthiness Model Implementation Application Areas

35 Application Areas Web services E-business within semantic grid

36 Definition Web service (WS) Software application identified by a URI XML artifacts: Interface definition and discovering Web Service Description Language (WSDL) Universal Description, Discovery, and Integration (UDDI) registry, ebXML Simple Object Access Protocol (SOAP)

37 Communities of WSs Gathering WSs with similar functionalities (e.g. FlightBooking ) Operations: How to initiate, set up, and specify a community of WSs? How to specify and manage the WSs that reside in a community? How to trust WSs within a community?

38 New Architecture of WSs Communities

39 Entry Game

40 Defense Game

41 E-business in Semantic Grid Argumentative agents for semantic grid (ArguGrid)

42 E-business in Semantic Grid

43 Programming the Grid Trust grid Environment Dialogue game protocols: specification, implementation, and verification Global View Argumentation-based Framework for Semantic Grid Communication, Negotiation and Persuasion between Grid Components

44 Future Work Evaluate the model using concrete scenarios in e-business settings A general framework for secure and verifiable grid-computing-based applications with the underlying formal semantics Trust in WS communities

Argumentation and Trust: Issues and New Challenges Jamal Bentahar Concordia University (Montreal, Canada) University of Namur, Belgium, June 26, 2007