Argumentation and Trust: Argumentation and Trust: Issues and New ChallengesIssues and New Challenges
Jamal BentaharConcordia University (Montreal, Canada)
University of Namur, Belgium, University of Namur, Belgium, June 26, 2007June 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
Mental Approach
Private states: Beliefs, Desires, Intentions, etc.
Social Approach
Social Approach
Public states: Social
commitments
Argumentative Approach
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
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Motivations
• How to trust negotiating agents within a multi-agent
system:
• Resources sharing and mutual access
Centralized Approaches
Vulnerable to attacks
Vulnerable to attacks Reasoning
CapabilitiesReasoning Capabilities
QuantitativeProbabilistic-based
QuantitativeProbabilistic-based
Decentralized Approach
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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
Agent 1Agent 1 Agent 2Agent 2
Social Commitments
+
Argumentation
Social Commitments
+
Argumentation
Speech Act Theory + Action Logic
Speech Act Theory + Action Logic
Negotiation
SpecificationSpecification
Reasoning + SemanticsReasoning + Semantics
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Negotiation Framework
Argumentation Theory
Agent Negotiation
SupportSupport
FlexibilityFlexibility EfficiencyEfficiency
Dialogue Games
Dialogue Games
RelevanceTheory
RelevanceTheory
Logic-based
Reasoning
Logic-based
Reasoning
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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//
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Dialogue Games: Specification
• Initiative / reactive dialogue games
• A simple language
• Cond: generating arguments from the agent’s argumentation system
Action_Ag1 Action_Ag2
Cond
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Dialogue Games: Specification
ConditionAction_Ag1 Action_Ag2
Create(Ag1,SC(p))
Accept(Ag2,SC(p))
Challenge(Ag2,SC(p))
Refuse(Ag2,SC(p))
Termination
Justification
Persuasion
c1
c2
c3
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Agent Communication
• Action_Agi {Make-Offer, Make-Counter-
Offer, Withdraw, Satisfy, Violate, Accept,
Refuse, challenge, Justify, Defend, Attack}
Argumentation system
Argumentation system
Communicative Actions
Communicative ActionsSupportsSupports
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• 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
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• The notion of argument:
a pair <Premises, Conclusion>
• 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
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• Attack relation: binary relation between
arguments
• An argument (P1, c1) attacks another
argument (P2, c2) iff
• c1 c2 or x P2 | c1 x
Argumentation Dynamics
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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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• Qualitative approach: Using argumentation to reason about trust
• Quantitative approach: Probability function• Rep : AAD [0, 1]
• Local beliefs
• Global beliefs: testimonies of witnesses
_ ( ) _ ( ) ( )
_ _ ( ) _ _ ( )a a
aa a
Ag Agb bAgb
Ag Agb b
Nb Arg Nb CAg AgRep Ag
T Nb Arg T Nb CAg Ag
Foundation
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Illustration
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• Central Limit Theorem and the Law of Large Numbers
• If M > w Then Return True
Else Return False
1
1
( ) ( ) ( ) ( )
( ) ( ) ( )a b b i
b ba
nAg Ag Ag Agi i i bi
nAg Agi i ii Ag
Rep N TR RepAg Ag Ag AgM
Rep N TRAg Ag Ag
Assessing Agent’s Reputation
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Timely Relevance Function
ln( )( )
AgbAgb i
i
tAgAgTR t e
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Reputation Graph
• Algorithm 1: Graph Construction
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Algorithm2: Node Evaluation
Evaluate-Node(Agy) { Arc(Agx, Agy)
If Node(Agx) is note evaluated Then Evaluate-Node(Agx)
m1 := 0, m2 := 0 Arc(Agx, Agy) {
m1 = m1 + Weight(Node(Agx)) * Weight(Arc(Agx, Agy)) m2 = m2 + Weight(Node(Agx))
} Weight(Node(Agy)) = m1 / m2
}
Algorithm 2
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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:
( )O n
( )O a
(max( , ))O a n
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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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Programming the Grid
Trust grid Environment
Dialogue game protocols: specification, implementation, and verification
Global View
Argumentation-based Framework for Semantic Grid
Argumentation-based Framework for Semantic Grid
Communication, Negotiation and Persuasion between Grid
Components
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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
Argumentation and Trust: Argumentation and Trust: Issues and New ChallengesIssues and New Challenges
Jamal BentaharConcordia University (Montreal, Canada)
University of Namur, Belgium, University of Namur, Belgium, June 26, 2007June 26, 2007