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Trust Based Mechanism Design

Trust Based Mechanism Design. Use MD. 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. . i. i. p. p. r. r. c. c. e. e. Y. X.

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Trust Based Mechanism Design

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  1. 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.

  4. i i p p r r c c e e Y X Deciding on a service provider Garage X is better than Y X Garage Y is better than X! Y

  5. Motivation WHICH GARAGE TO EMPLOY? X Y

  6. 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.

  7. 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

  8. 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

  9. 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

  10. Cheapest not always best …..

  11. i [ ( ) ] µ E C K ´ v i 4 4 4 ; Adding uncertainties • Suppose that agent 4 has formulated a belief about the Probability of Success (POS) of other agents.

  12. Trust • So far : one’s 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 everyone’s experience

  13. 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

  14. [ ( [ ) ] ] ( ) µ E j 0 3 0 2 0 1 0 4 2 1 0 1 ® v v ¿ = = 4 4 4 ; : : : : ; i 3 2 1 t ´ ´ ´ 4 i i i c i Incorporate Trust VCG Fails!!

  15. b ¤ K 5 8 4 0 0 0 c c c = = = 1 3 2 i i i i ´ ´ ´ ´ 4 2 3 1 Centre calculates optimal allocation 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

  16. b ( ) ( ) ¤ ¤ ¤ K D U K U K ¡ = i i i ¡ ¡ 8 4 5 0 0 0 ; : ; : c c c = = = 3 2 1 i i i i ´ ´ ´ ´ 4 1 2 3 Centre calculates optimal allocation without each agent i’s POS report. TBMD (£210,task1) Trust model Centre 4 3 1 2

  17. D ¡ r m c = i i i 4 8 5 0 0 0 c c c = = = 2 1 3 ¤ K i i i i r i ; ´ ´ ´ ´ 3 2 4 1 Centre calculates transfer to i , TBMD (£210,task1) Trust model Centre 4 3 1 2

  18. Steps in TBMD

  19. 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

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

  21. Results K* K*TBM K*TBM0.25 K*VCG K*TBM0.5 K*FTM

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

  23. End rkd02r@ecs.soton.ac.uk Any Questions?

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