Analyzing Control Trust in Normative Multiagent Systems

Joris Hulstijn1 jhulstijn@feweb.vu.nl

Yao-Hua Tan1 ytan@feweb.vu.nl

Leendert van der Torre2 torre@cwi.nl

1. Vrije Universiteit, Amsterdam2. CWI, Amsterdam and Delft University of Technology

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Transaction Trust(Tan & Thoen 2000, 2002)

1. How can we model control trust? 2. How does control trust affect transaction trust?

Transaction Trust

Trust in other Party

Trust in control mechanisms

Potential Gain

Risk & Risk Attitude

Personal Relationship

Role-based

Reputation

Trust in institution

Understanding control mechanism

extern

intern

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How? • Recursive modeling: model the decision making of

trustor, taking profiles of trustee, and of a normative system, into account

trustor

trustee

$$

normative system

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Normative Multiagent Systems

(Jones & Carmo 2002)• Normative Multiagent Systems are

– sets of agents,– whose interaction can be regarded as norm

governed. – Norms describe an ideal situation, – but actual situations can deviate from the ideal

(violations).

• Model normative system n, as an agent.

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Overview• Case: Letter of Credit

– international trade similar to E-commerce

• Normative MultiAgent Systems– beliefs and goals– constitutive and regulative norms

• Analysis– contrast situation with and without control

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Case: Letter of Credit(Bons 1997, Lee 2000, Kartseva et al 2004)

1. lack of trust replaced by banking relation

2. evidentairy documents, guaranteed by UN.

customer suppliercarrier

issuing bank

corresp. bank

1. Sales contract

2. credit appl.

3. credit

4. creditnotif.

5. goods

6. shipping docs

7. shipping docs

8. payment

9. shipping docs

10. payment

11. arrival notif

12. payment13. shipping docs

14. shipping docs

15. goods

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NMAS 1: Beliefs and Goals

• Focus on goal generation• Production rules A B

represent beliefs and goals, with a priority order <.

• Belief rules: current state• Goal rules: desired state

(through actions)

<BeliefsGoals

Observations

Actions

Goals

GoalGeneration

Planning &Scheduling

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NMAS 1: Beliefs and Goals• Example

• Belief: at party Goal 1: at party smoke Goal 2: not smoke

• Priority: Belief > Goal 1 > Goal 2

• Priority: Belief > Goal 2 > Goal 1

Outcome: { at party , smoke }

Outcome: { at party , not smoke }

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NMAS 2: Constitutive Norms(Searle 1995)

• Constitutive norms are used to model the evidentiary documents.

• For all a: x counts as y in context C.• For all a: shipping docs and no shipping counts as

fraud in the context of LC.

• Belief of a:

LC & (shipping docs & not shipping) fraud

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NMAS 3: Regulative Norms(Boella and van der Torre 2004)

• “Your wish is my command”• Agent a is obliged to n to do x in context C, against a

sanction s. • Carrier is obliged to issuing bank that no fraud occurs

in the context of LC, against the sanction of a law suit:1. Goal of ib: LC not fraud

2. Goal of ib: LC & fraud Viol(fraud,ca) detect

3. Goal of ib: not Viol(fraud ,ca)

4. Goal of ib: LC & Viol(fraud ,ca) law suit sanction

5. Goal of ib: not law suit

6. Goal of ca: not law suit deter

7. Goal of ca: fraud7. Goal of ca: fraud

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NMAS 3: Regulative NormsCustomer’s profile:

ca’s profile of ib: goal 1-5,

ca: goal 6, 7

{ LC, fraud, not law_suit }.

ca’s profile of ib: goal 2 > goal 3 (detect)

{ LC, fraud, not law_suit, Viol(fraud,ca) }.

ca’s profile of ib: goal 4 > goal 5 (sanction)

{LC, fraud, not law_suit, Viol(fraud ,ca), law_suit}

Conflict, resolve by ca: goal 7 > goal 6

{ LC, fraud, Viol(fraud, ca), law_suit }

But if ca: goal 6 > goal 7 (deter)

{ LC, not law_suit }

So customer will trust carrier, if detect, sanction and deter hold.

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Analysis 1: No Letter of Credit

• In the absence of party trust and controls– Customer is obliged to supplier to pay at shipping,

against an ‘internal sanction’ of being in debt. – Supplier is obliged to customer to ship at payment,

against an ‘internal sanction’ of being in debt.

– Profile of supplier: Goal of customer: not payment > not in debt

– Profile of buyer: Goal of supplier: not shipping > not in debt

• ... no transaction!

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Analysis 2: With Letter of Credit

• Direct Transaction (same time, location)– Customer is obliged to supplier to pay at shipping,

against a ‘sanction’ of no shipping.

– Supplier is obliged to customer to ship at payment, against a ‘sanction’ of no payment.

• Indirect Transaction (distant in time, location)– Customer is obliged to n to pay at evidence of

shipping, against a sanction of no delivery.

– Supplier is obliged to n to ship at evidence of credit, against a sanction of no payment.

• Similar principles apply to E-commerce

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Conclusions• Model control trust by

– regulative norms, seen as violation detection and sanctioning goals of a normative system,

– constitutive norms for evidentiary documents.

• Control trust affects transaction trust, when in the trustor's profile of the trustee, – the normative system will actually detect and

sanction violations, and – the trustee prefers to avoid sanctions.

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Conclusions• To design control mechanisms for E-commerce

– Use standards for evidentiary documents, maintained by an institution that has the power to apply credible sanctions.

– Start with a mutual obligation (direct transaction), in which the sanction for one party is non-compliance of the other party.

– Create a causal chain (indirect transaction) in which evidence of compliance can replace compliance.