mechanisms to promote cooperation in decentralized services
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Outline System Model Cooperation Mechanisms Results Conclusions
Mechanisms to promote cooperationin decentralized services
E. del Val M. Rebollo V. Botti
Univ. Politecnica de Valencia (Spain)
EUMAS ’12Dublin, December 2012
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Promoting Cooperation
MotivationThere are scenarios in decentralized systems in which cooperationplays a central role
agents connected in networksbounded rationalityheterogeneous, self-interested agents
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Our Proposal
The challengeObtain an emergent, cooperative global behavior even whencooperators are a minority, from local decisions.
What is done. . .a network structure that ensures navigation and efficiencystructural changes to isolate undesired agentsincentives to promote cooperation
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Outline
1 Outline
2 System Model
3 Cooperation Mechanisms
4 Results
5 Conclusions
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
System Model
Definition (Open Service-Oriented MAS)
(A, L), where A = {ai , ..., an} is a finite set of autonomous agentsthat are part of the system, and L ⊆ A× A is the set of links,where each link (ai , aj) ∈ L
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
System Model
Definition (Agent)
is a tuple (Si ,Ni , sti ) where:Si = {s1, . . . , sl} is the set of semantic service descriptions ofthe services provided by the agent (WSDL);Ni is the set of neighbors of the agent,Ni ⊆ A− {ai} : ∀aj ∈ Ni , ∃(ai , aj) ∈ L, and |Ni | > 0. It isassumed that |Ni | � |A|;sti is the internal state of the agent.πi : sti → Ni is the neighbor selection function thatdetermines the most promising neighbor to provide a service;ρi : sti → Ψ is the adaptation selection function where Ψ isthe set of finite adaptation actions of the agent.
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Network Creation
probabilistic relations baed on homophily (assortativity,similarity)two agents are similar if they provide similar services
H = αHv + (1− α)Hs
growing network structure (exponential degree distribution)certain characteristics of a small-world network (short paths,clustering)
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Service Discovery
navigation problem in networks (it relies in the agentcooperation)hill climbing (greedy) method
π(at) = argmaxaj∈Ni
1−1−
H(aj , at)∑an∈Ni
H(an, at)
|Nj |
agents pass the query until the desire service is foundit is a problem with self–interested agents
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Social Plasticity
capacity to changerelations as times passeslink utility decays withtimedepends on the queries ajforwards
D(aj) = 11+e−γ
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Social Plasticity
when an agent breaks a link, a substitute must be found(maintain the network structure)criteria
neighbor of neighbora similar agent to the previous one
rewire links has not a cost
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Social Plasticity
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Social Plasticity
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Incentives
each action implies a cost (ask for a service and forward)a reward is obtained if the service is foundrewards are provided by the systemagents imitated the strategy of successful neighbors
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Incentives
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Combining social plasticity and incentives
Both strategies promote cooperation in generalbut it is not enough if non–cooperative agents has a highdegree
network broken in isolated partsrewire cost –> not affordable for some agentspayoff not enough to promote cooperation
the combined model1 incentives to change the behavior of non–cooperatives2 rewire links if it fails
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Experiment Design
Configuration
1,000 agents, 10 different networks100 steps to forward a query, snapshots after 5,000 queriesvarying the initial prop. of collaborators
Strategies
Social plasticity (SP)IncentivesReinforcement Learning (RL) using WOLFGame-theory approach, using Prisoner’s Dilemma (PD)Incentives + Social Plasticity (I+SP)
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Measures
proportion of collaborator / non–collaboratorsaverage path length (better if smaller)search failures due to non–collaborationsearch success (including TTL)
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
60% of collaborators (num and path length)
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
40% of collaborators (num and path length)
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
60% of collaborators (failures and success)
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
40% of collaborators (failures and success)
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
Outline System Model Cooperation Mechanisms Results Conclusions
Conclusions
improving cooperation to solve navigation problem in networksapplied to decentralized service managementcombination of structural changes and incentivesimproves the performance when non-collaborators are’important’ in the networkworks by imitation: a core of collaborators is neededa guess: the size of the core depends on networkcharacteristics (percolation, efficience, centrality coefficient)
M. Rebollo et al. (UPV) EUMAS’12Mechanisms to promote cooperation in decentralized services
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