Argumentation and Trust: Issues and New Challenges

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Argumentation and Trust Issues and New
Challenges

• Jamal Bentahar
• Concordia University (Montreal, Canada)

University of Namur, Belgium,
June 26, 2007
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Overview

• Problem and Motivations
• Negotiation Framework
• Trustworthiness Model
• Implementation
• Application Areas

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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

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Proposed Approaches for Interacting Agents
Mental Approach
Social Approach
Argumentative Approach
Private states Beliefs, Desires, Intentions, etc.
Public states Social commitments
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
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Motivations

• How to trust negotiating agents within a
  multi-agent system
• Resources sharing and mutual access

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Overview

• ? Problem and Motivations
• Negotiation Framework
• Trustworthiness Model
• Implementation
• Application Areas

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Agent Architecture
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Negotiation Framework
Specification
Reasoning Semantics
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Negotiation Framework
Argumentation Theory
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Dialogue Games

• Abstract structures that can be composed
• Sequencing
• Embedding
• Parallelization
• Argumentation-driven decision making process

Game 1
Game 2
,
//
Game 1
Game 2
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Dialogue Games Specification

• Initiative / reactive dialogue games
• A simple language
• Cond generating arguments from the agents
  argumentation system

Cond
Action_Ag1
Action_Ag2
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Dialogue Games Specification
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Agent Communication

• Action_Agi ? Make-Offer, Make-Counter-Offer,
  Withdraw, Satisfy, Violate, Accept, Refuse,
  challenge, Justify, Defend, Attack

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Argumentation

• 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.

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Formal Argumentation

• The notion of argument
• a pair ltPremises, Conclusiongt
• 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

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Argumentation Dynamics

• Attack relation binary relation between
  arguments
• An argument (P1, c1) attacks another argument
  (P2, c2) iff
• c1 c2 or x P2 c1 x

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Argumentation Dynamics
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Overview

• ? Problem and Motivations
• ? Negotiation Framework
• Trustworthiness Model
• Implementation
• Application Areas

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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

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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

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Foundation

• 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

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Illustration
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Assessing Agents Reputation

• Central Limit Theorem and the Law of Large
  Numbers
• If M gt w Then Return True
• Else Return False

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Timely Relevance Function
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Reputation Graph

• Algorithm 1 Graph Construction

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Algorithm2 Node Evaluation
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Complexity

• Construction of the trust graph with n nodes and
  a edges
• n recursive calls of the function Evaluate-Node
  (Agy)
• 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

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Overview

• ? Problem and Motivations
• ? Negotiation Framework
• ? Trustworthiness Model
• Implementation
• Application Areas

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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

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System Architecture
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Architecture of Negotiating Agent
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Overview

• ? Problem and Motivations
• ? Negotiation Framework
• ? Trustworthiness Model
• ? Implementation
• Application Areas

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Application Areas

• Web services
• E-business within semantic grid

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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)

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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?

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New Architecture of WSs Communities
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Entry Game
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Defense Game
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E-business in Semantic Grid

• Argumentative agents for semantic grid (ArguGrid)

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

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Argumentation and Trust Issues and New
Challenges

• Jamal Bentahar
• Concordia University (Montreal, Canada)

University of Namur, Belgium,
June 26, 2007