Examining Dynamic Trust Relationships in Autonomy-Oriented Partner Finding Department of Computer Science, HKBU, HK International WIC Institute, BJUT, China Student ： Hongjun Qiu Supervisor ： Prof. Jiming Liu Aug. 31, 2009

Finding partners: to identify which can provide services as needed – the limited abilities of entities. Partner finding in cloud computing –The cloud: the Internet –The servers need response to hundreds or thousands of requests of data storage, program running and so on per second. –Each user can ask more than one servers to immediately do their tasks. Partner Finding The International WIC Institute, BJUT, China References: [1] [2] B. Hayes, cloud computing, Communication of the ACM, 51(7): 9-11, [3] M. Greeger, CTO roundtable: Cloud computing, Communications of the ACM, 52(8): 50-56, 2009.

A solution of partner finding: dynamically measuring and changing trust relationships. –Trust relationships: the beliefs that others will accomplish a request of assigned services at hand. –Computing methods: based on recalling their past experiences –Advantages: quickly identify partners for new requests. Trust Relationships The International WIC Institute, BJUT, China References: [1] Jennifer. Golbeck, Weaving a web of trust, Science, 321(5896): , [2] S. D. Kamvar, M. T. Schlosser and H. Garcia-Molina. The Eigentrust Algorithm for Reputation Management in P2P Networks. In: Proceedings of the 12th International Conference on World Wide Web (WWW’03). 2003, 640 – 651. [3] eBay

Questions The International WIC Institute, BJUT, China Goal: to determine whether the change of trust relationships will really make entities efficiently find partners Questions to be answered: How do entities update their trust relationships? What are the mechanisms for entities find partners? What is the change of trust relationships in a distributed multi- entity network? Will the efficiency of finding partners really get enhanced along with the change of trust relationships? −Will entities find partners in a fewer time? −Will found partners successfully provide services?

Basic phenomena: –Entities prefer to interact with their trustees rather than strangers. –Successful interactions strengthen trust relationships and vice versa. Assumptions: –A dynamic trust network: Nodes: entities –fixed and limited abilities –Friendly and honestly Links: trust relationships –Entities can find a partner to finish or transfer the whole request, which cannot be finished by themselves. The Scenario We Study The International WIC Institute, BJUT, China

To model a dynamic trust network –Define the mechanisms for finding partners –Define the mechanisms for updating trust relationships To characterize the change of trust relationships –the structural characteristics of this network at different moments To measure whether the efficiency of this network in finding partners changes along with the dynamics of trust relationships Questions The International WIC Institute, BJUT, China

A Dynamic Trust Network Hongjun Qiu The International WIC Institute, BJUT, China Entity Trust relationship

The Steps of Finding Partners Hongjun Qiu The International WIC Institute, BJUT, China a request Matching: determine whether it can finish this request 1 Search and selection: find a partner to finish the whole request 2 Updating: the asker updates its trust relationships 3 feedback propagation Entity Trust relationship

Two ideas from AOC Hongjun Qiu The International WIC Institute, BJUT, China a request Matching: determine whether it can finish this request Search and selection: find a partner to finish the whole request Updating: the asker updates its trust relationships autonomy Self- organizatio n Autonomy-Oriented Computing (AOC) References: [1] Jiming Liu, Xiaolong Jin, Kwok Ching Tsui. Autonomy-Oriented Computing (AOC): Formulating Computational Systems With Autonomous Components, IEEE Transactions on Systems, Man, and Cybernetics-Part A: Systems and Humans, Vol. 35, No. 6 (2005) [2] Jiming Liu, Xiaolong Jin, Kwok Ching Tsui. Autonomy Oriented Computing–From Problem Solving to Complex Systems Modeling, Springer Series on Multiagent Systems, Artificial Societies, and Simulated Organizations Vol. 12,(2005)

Basic idea: entities activate different behaviors in a probabilistic manner based on measuring their abilities, requests and trust relationships Search behaviors –Neighbor-based search –Recommendation-based search –Random search: for new comers to this network Selection behaviors –Trust-based select –Random select The Local Autonomy of Entities Hongjun Qiu 1) The probability of activating each behavior is adaptive; 2) Entities mainly find partners from their trustees for the requests which are near to their abilities. The cosine-based similarity degree between the ability of this entity and this request

Basic rules: –change trust relationships based on the feedback from the latest partner of an entity. –Strengthen trust relationships if the partner is more suitable for the latest request Operations –Creating trust relationships if the partner is newly-found. –Updating existing trust relationships if the partner is one of the past partners of this entity. –Eliminating the trust relationships to its other past partners if their strength are less than a threshold. Self-organizing Trust Relationships

Introduced: a dynamic trust network Experiments: –To characterize the change of trust relationships by means of observing the dynamic links of this network Network structural characteristics –To determine whether the efficiency of this network in finding partners gets enhanced by means of comparing the efficiency at different moments Without trust relationships, With newly-generated trust relationships With frequently-changed trust relationships Experimental Objectives

Given: –A trust network of 1000 entities, without links –Requests 100 fixed requests Basic process 1.For( cycle=0; cycle<1500; cycle++) 2. For( i=0;i<100; i++) 3. Stochastically submit the ith request to the network 4. Find partners within given times to finish this request 5. End for 6. Stochastically submit one random request to the network 7. Update trust relationships while finding partners for this request 8.End for Experimental Settings The International WIC Institute, BJUT, China

To measure structural characteristics at different cycles –Network indegree/outdegree –Harmonic mean of average path length –Clustering coefficient To measure the efficiency of entities in finishing the same 100 requests at different cycles –The accomplishment ratio –The average propagation step: the times entities find partners –The standard deviation of propagation step Experimental Measurements The International WIC Institute, BJUT, China

The Dynamics of the Network Hongjun Qiu The International WIC Institute, BJUT, China Cycle=0Cycle=1500

The Dynamics of the Structure Hongjun Qiu Results and discussions: 1. The values of network indegree (outdegree), harmonic mean of average path length, clustering coefficient increase rapidly at first and later change slightly. 2. Entities greatly change their trust relationships at first and then maintain parts of those relationships.

The Structural Emergence Hongjun Qiu Results and discussions: 1. Entities’ indegree (outdegree) approximately follow a power-law distribution since about the 16 th cycle. 2. The process of self-organization makes the network quickly converge to be scale-free.

The Change of the Efficiency The accomplishment ratio in each cycle and each 10 cycles The average propagation step in each cycle and each 10 cycles The standard deviation of propagation step in each cycle and each 10 cycles Results and discussions: 1.The accomplishment ratio gradually increases. 2.The average value and standard deviation of propagation step gradually decrease. 3.In the later cycles, entities can more quickly find partners to provide services with a higher probability. 4.In the later cycles, entities have found their relatively partners and they are coupled together.

Experimental results –The network quickly converges to be scale-free, no matter what distribution the abilities follow; –Trust relationships are frequently changed at first and remain stable later; –The efficiency is enhanced along with dynamic trust relationships. Conclusions –Trust relationships are changed toward a certain state, in which entities quickly find partners to successfully provide services. –The ideas from AOC speed up the change of trust relationships. Concluding Remarks

Thank You!