在行動社交網路中維持資料的一致性是必要的。Delta Consistency (DC) 讓使用者更彈性的制定對資料一致性的需求。在DC 中，請求者(requester)和資料來源者(source)的資料在某一段時間內不同是可以允許的。這某一段時間稱作容忍時間(Delta Time)。在過去的研究中，僅假設每個請求者只能根據資料來源者的特性來設定容忍時間，這使得每個請求者的容忍時間都相同，這個假設忽略了請求
者本身對源資料(source data)一致性的需求。然而在實際情形中，每個人對於同一份資料的一致性程度應當不同，所以本篇論文在請求者設定容忍時間時，除了
考慮資料來源者的特性之外，還會考慮請求者對於源資料的需求。為了滿足不同
請求者的需求，提供一個適當的資料一致性機制給來源者就顯得很重要。本篇論
文考量了不同使用者對於源資料一致性會有不同的需求而提出了可變動的維護
資料一致性演算法(FCMA)。除此之外還會選出一些輔助點(Supporting Nodes)來幫忙傳遞和暫存資料。FCMA 會先判斷請求者在收到資料時是否還在容忍時間內，接著根據判斷的結果來決定適當的資料維護機制，進而節省資料維護成本。實驗結果顯示FCMA 確實可以比其他機制花費更少的成本來滿足請求者的需求。

Data consistency is an important issue in Mobile social networks. Delta consistency (DC) has been proposed for fulfilling flexible data consistency requirements. In DC, the deviations of data version between source and requester can be accepted during a specific length of time. The specific length of time is named as delta time. In previous research, each requester sets same delta value according to data characteristic and application, i.e. each requester has same consistency requirement to same data. This assumption ignores user interests to the data. In real world, different people should have different interest on the same thing. Therefore, the consistency requirement of each requester should not only set based on data application but also set based on personal interest. Then each requester will have different consistency requirement to same data and it would be highly desirable to provide source a flexible scheme for meeting different consistency requirements. This thesis takes the personal interest into consideration and proposes “Flexible Consistency Maintenance Algorithm” (FCMA) which can satisfy different consistency requirements with adaptive cost. Furthermore some supporting nodes are selected to increase data dissemination and access. The basic idea is that source intentionally predicts whether data will expire or not when requester receives data. Then source decides a suitable consistency maintenance scheme according to the predicative result. Simulation results show that FCMA can satisfy varying consistency requirements and require less maintenance cost.

[1] A. Chaintreau, P. Hui, J. Crowcroft, C. Diot, R. Gass, and J. Scott, “Pocket Switched Networks and Human Mobility in Conference Environments,” in Proceedings of ACM SIGCOMM Workshop on Delay-Tolerant Networking (WDTN), Aug. 2005, pp. 244–251.
[2] M. Motani, V. Srinivasan, and P. S. Nuggehalli, “Peoplenet: Engineering A Wireless Virtual Social Network,” in Proceedings of International Conference on Mobile Computing and Networking (MobiCom), Aug. 2005, pp. 243–257.
[3] K. Fall, “A Delay-Tolerant Network Architecture for Challenged Internets,” in Proceedings of Conference on Applications, Technologies, Architectures, and Protocols
for Computer Communications, Aug. 2003, pp. 27–34.
[4] A. Anders, A. Doria, and O. Schelen, “Probabilistic Routing in Intermittently Connected Networks,” ACM SIGMOBILE Mobile Computing and Communications Review, vol. 7, no. 3, pp. 19–20, July 2003.
[5] W. Gao, G. Cao, A. Iyengar, and M. Srivatsa, “Supporting Cooperative Caching in Disruption Tolerant Networks,” in International Conference on Distributed Computing Systems (ICDCS), June 2011, pp. 151–161.
[6] K. J. Lin, C. W. Chen, and C. F. Chou, “Preference-Aware Content Dissemination in Opportunistic Mobile Social Networks,” in International Conference on Computer
Communications (INFOCOM), Mar. 2012, pp. 1960–1968.
[7] P. Costa, C. Mascolo, M. Musolesi, and G. P. Picco, “Socially-Aware Routing for Publish-Subscribe in Delay-Tolerant Mobile Ad Hoc Networks,” IEEE Journal on Selected Areas in Communications, vol. 26, no. 5, pp. 748–760, June 2008.
[8] H. Chen and W. Lou, “On Using Contact Expectation for Routing in Delay Tolerant Networks,” in International Conference on Parallel Processing (ICPP), Sept. 2011,
pp. 683–692.
[9] W. Gao and G. Cao, “User-Centric Data Dissemination in Disruption Tolerant Networks,” in International Conference on Computer Communications (INFOCOM), Apr. 2011, pp. 3119–3127.
[10] W. Gao, Q. Li, B. Zhao, and G. Cao, “Multicasting in Delay Tolerant Networks: A Social Network Perspective,” in Proceedings of International Symposium on Mobile Ad Hoc Networking and Computing (MobiHoc), May 2009, pp. 299–308.
[11] W. Gao, G. Cao, M. Srivatsa, and A. Iyengar, “Distributed Maintenance of Cache Freshness in Opportunistic Mobile Networks,” in International Conference on Distributed Computing Systems (ICDCS), June 2012, pp. 132–141.
[12] J. Cao, Y. Zhang, G. Cao, and L. Xie, “Data Consistency for Cooperative Caching in Mobile Environments,” Computer, vol. 40, no. 4, pp. 60–66, Apr. 2007.
[13] J. Cao, Y. Zhang, L. Xie, and G. Cao, “Consistency of Cooperative Caching in Mobile Peer-to-Peer Systems over MANET,” in International Conference on Distributed
Computing Systems Workshops, June 2005, pp. 573–579.
[14] Y. Huang, J. Cao, B. Jin, X. Tao, J. Lu, and Y. Feng, “Flexible Cache Consistency Maintenance over Wireless Ad Hoc Networks,” IEEE Transactions on Parallel and Distributed Systems, vol. 21, no. 8, pp. 1150–1161, Aug. 2010.
[15] A. Vahdat and D. Becker, “Epidemic Routing for Partially Connected Ad Hoc Networks,” Duke University, Tech. Rep. CS-200006, July 2000.
[16] T. Spyropoulos, K. Psounis, and C. Raghavendra, “Spray and Wait: An Efficient Routing Scheme for Intermittently Connected Mobile Networks,” in Proceedings of ACM SIGCOMM Workshop on Delay-Tolerant Networking (WDTN), Aug. 2005,
pp. 252–259.
[17] ——, “Spray and Focus: Efficient Mobility-Assisted Routing for Heterogeneous and Correlated Mobility,” in International Conference on Pervasive Computing and
Communications Workshops, Mar. 2007, pp. 79–85.
[18] V. Erramilli, M. Crovella, A. Chaintreau, and C. Diot, “Delegation Forwarding,” in Proceedings of International Symposium on Mobile Ad Hoc Networking and Computing (MobiHoc), May 2008, pp. 251–260.
[19] A. Balasubramanian, B. Levine, and A. Venkataramani, “DTN Routing as a Resource Allocation Problem,” in Proceedings of Conference on Applications, Technologies, Architectures, and Protocols for Computer Communications, Aug. 2007,pp. 373–384.
[20] P. Hui, J. Crowcroft, and E. Yoneki, “Bubble Rap: Social-Based Forwarding in Delay-Tolerant Networks,” IEEE Transactions on Mobile Computing, vol. 10, no. 11,
pp. 1576–1589, Nov. 2011.
[21] P. Hui, E. Yoneki, S. Chan, and J. Crowcroft, “Distributed Community Detection in Delay Tolerant Networks,” in Proceedings of International Workshop on Mobility in The Evolving Internet Architecture (MobiArch), July 2007.
[22] Y. Zhang, J. Zhao, G. Cao, and C. Das, “On Interest Locality in Content-Based Routing for Large-Scale MANETs,” in International Conference on Mobile Ad-hoc and Sensor Systems (MASS), Oct. 2009, pp. 178–187.
[23] H. Zhang and H. Shen, “A Social Network Based File Sharing System in Mobile Peer-to-Peer Networks,” in Proceedings of International Conference on Computer
Communications and Networks (ICCCN), Aug. 2009, pp. 1–6.
[24] L. Yin and G. Cao, “Supporting Cooperative Caching in Ad Hoc Networks,” IEEE Transactions on Mobile Computing, vol. 5, no. 1, pp. 77–89, Jan. 2006.
[25] S. Zhu and C. Ravishankar, “Stochastic Consistency, and Scalable Pull-Based Caching for Erratic Data Stream Sources,” in Proceedings of International Conference on Very Large Data Bases (VLDB), Aug. 2004, pp. 192–203.
[26] H. Shen, “IRM: Integrated File Replication and Consistency Maintenance in P2P Systems,” IEEE Transactions on Parallel and Distributed Systems, vol. 21, no. 1,
pp. 100–113, Jan. 2010.