Trust Based Mechanism Design

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Trust Based Mechanism Design
2
Use MD
3
Motivation

• Fuse the fields of trust-modelling and mechanism
  design
• Trust measures how good an interaction partner is
  
• Mechanism design concerns itself with the
  allocation of resources.

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Deciding on a service provider
Garage X is better than Y
X
Garage Y is better than X!
Y
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Motivation
WHICH GARAGE TO EMPLOY?
X
Y
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Mechanism Design

• The design of systems of interacting agents
• Protocols (allocation payment schemes) to
  ensure that certain global properties are
  achieved at equilibrium (game-theoretic).
• Selfish, rational agents possessing private
  information i.e. each agent maximises its utility
  function given its type.

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Task Allocation

• Agent 4 wants a task to be completed.
• Problem
• Who to allocate task to ?
• How much to pay task performer ?
• Solution
• VCG mechanism

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Applying VCG
Centre
(210,task1)
Allocate task to 1, 4 pays 1 50
4
Ask(40,task1)
Ask(50,task1)
Ask(80,task1)
1
2
3
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VCG Mechanism

• Class of mechanisms satisfying
• Efficiency outcome maximising utility for all
  agents
• Individually rationality incentivise
  participation
• Incentive compatibility incentivise truthful
  report
• under dominant strategy
• Works by
• Allocation choose allocation maximising utility
• Payment charge marginal utility contributed by
  agent

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Cheapest not always best ..
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Adding uncertainties

• Suppose that agent 4 has formulated a belief
  about the Probability of Success (POS) of other
  agents.

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Trust

• So far ones own experience.
• Would be better to factor in others experiences
  as well.
• First time agent
• Greater pool of experience for seasoned user.
• Trust a way of aggregating everyones experience

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Our model of trust

• Each time a task is performed, record POS
• Publicly transmit the POS to other agents
• Trust
• Use a simple averaging function over reports from
  all agents
• Give more weight to more trusted referrals, or
  agents with similar properties

4
2
3
1
Record POS
Transmit POS
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Incorporate Trust
VCG Fails!!
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TBMD
(210,task1)
Trust model
Centre
4
3
1
2
4 transmits to centre -- value of task, observed
POS and trust model
1, 2, 3 transmit to centre -- cost of doing task
and observed POS
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TBMD
(210,task1)
Trust model
Centre
4
3
1
2
17

TBMD
(210,task1)
Trust model
Centre
4
3
1
2
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Steps in TBMD
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Trust Based Mechanism Design (TBMD)

• An individually rational and efficient ICDR
  mechanism that can also select those agents that
  are most successful at their task

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Experimental Setup

• Set of buyers and sellers.
• Biased (but truthful!) report from seller.
• Buyers attach different levels of importance to
  sellers report.

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Results
K
KTBM
KTBM0.25
KVCG
KTBM0.5
KFTM
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Conclusions

• Task allocation with uncertainty.
• Only incentive-compatible, individually-rational
  efficient reputation mechanism.
• Works with a very large class of trust models.

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End
rkd02r_at_ecs.soton.ac.uk

• Any Questions?