Barbar'a D., Garcia-Molina H. "Replicated Data Management in Mobile Environments: Anything New Under the Sun ?," Proc. IFIP Conf. on Applications in Parallel and Distributed Computing, Caracas, Venezuela, April 1994.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....requirements. These services mainly address the management of the data objects and files in the presence of mobility. They are also responsible for negotiating with MSSs the quality of the service according to both user requirements and services actually supplied by the wireless network [7, 13, 15, 22, 28, 29, 32]. The problem of locating MHs, i.e. of knowing their current position to allow the routing of the messages, has received great attention [5, 25] and is emphasized by the trend of reducing the cell s size to improve the communication bandwidth. Location service is architecturally located within ....

....caches, see Figure 1.3(a) Read Only Transactions: MHs only cache data objects for queries, and updates are performed as in the preceding case, see Figure 1. 3(b) Weak Transactions: Besides performing queries on cached data, MHs may update data objects in their caches even while disconnected [7, 28, 30, 40] see Figure 1.3(c) In this case, they must stabilize their updates as soon as they re connect, that is, they have to globally commit the updates in order to re establish consistency and to guarantee durability. For the purpose of stabilizing the disconnected transactions or undoing them in the ....

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Barbar'a D., Garcia-Molina H. "Replicated Data Management in Mobile Environments: Anything New Under the Sun ?," Proc. IFIP Conf. on Applications in Parallel and Distributed Computing, Caracas, Venezuela, April 1994.

....Three alternative locations for placing copies: the server, the mobile client, and the location servers for the client [3] Main consideration: the search cost to locate copies at mobile hosts. Dynamic algorithms for replicated data placement simply by letting transactions update the directory [7] To locate copies, transactions first obtain read locks on the directory. A change in the placement of copies is an update transaction on the directory. E. Pitoura Summer School on Mobile Computing, Jyvaskyla, 1998 28 Mobility Moving Computations Issues transparently from the ....

D. Barbar'a and H. Garcia-Molina. Replicated Data Management in Mobile Environments: Anything New Under the Sun? In Proceedings of the IFIP Conference on Applications in Parallel and Distributed Computing, April 1994.

....to define special protocols for such an environment. Summarizing the approaches, we state that there are the well known strategies extended with few mobility supporting mechanisms. Approaches offer a range of concepts from restricting the mobile work over lazy consistency to mobile work reserved. [BGM94] attempted to solve replication problems in mobile environments with exiting replication techniques. They distinguished between updateable core copies for read and write access, read only cached copies, and the directory to manage the copies. Updating the directory implied a reorganization of the ....

....us to be more sufficient than an arbitrarily selected d. While the availability of this approach in case of disconnections is high, consistency and costs depend on the r w pattern of core copies. Using a primary copy on a mobile disconnected site makes it impossible to update the other sites. [BGM94] proposed to combine the primary copy strategy with frequent backups to a cached copy . FZS95] developed a primary copy strategy especially for this problem, the Virtual Primary Copy. The Home Base Node contains the virtual primary copy as representative for the disconnected primary copy (VPC) ....

D. Barbar'a and H. Garcia-Molina. Replicated data management in mobile environments: Anything new under the sun? In IFIP Conference on Applications in parallel and Distributed Computing, 1994.

....to define special protocols for such an environment. Summarizing the approaches, we state that there are the well known strategies extended with few mobility supporting mechanisms. Approaches offer a range of concepts from restricting the mobile work over lazy consistency to mobile work reserved. [2] attempted to solve replication problems in mobile environments with exiting replication techniques. They distinguished between updateable core copies for read and write access, read only cached copies, and the directory to manage copies. Updating the directory implies a reorganization of core ....

....us to be more sufficient than an arbitrarily selected d. While the availability of this approach in case of disconnections is high, consistency and costs depend on the r w pattern of core copies. Using a primary copy on a mobile disconnected site makes it impossible to update the other sites. [2] proposed to combine the primary copy strategy with frequent backups to a cached copy . 5] developed a primary copy strategy especially for this problem, the Virtual Primary Copy. The Home Base Node contains the virtual primary copy as representative for the disconnected primary copy (VPC) ....

D. Barbar'a and H. Garcia-Molina. Replicated data management in mobile environments: Anything new under the sun? In IFIP Conference on Applications in Parallel and Distributed Computing, 1994.

....are ignorant of strict and weak transactions at other clusters. The techniques of supporting N ignorance can be incorporating in the proposed model to define d as the ignorance factor N of weak transactions. Mobile Database Systems. The effect of mobility on replication schemes is discussed in [2]. The need for the management of cached copies to be tuned according to the available bandwidth and the currency requirements of the applications is stressed. In this respect, d degree consistency and weak transactions realize both the above requirements. The restrictive nature of one copy ....

D. Barbar'a and H. Garcia-Molina. Replicated Data Management in Mobile Environments: Anything New Under the Sun? In Proceedings of the IFIP Conference on Applications in Parallel and Distributed Computing, April 1994.

....the number of updates. In [29] a generalization of ESR was proposed for high level type specific operations on abstract data types. In contrast, our approach deals with low level read and write operations. Mobile information Systems. The effect of mobility on replication schemas is discussed in [2]. The need for the management of cached copies to be tuned according to the available bandwidth and the currency requirements of the applications is stressed. In this respect, d degree consistency and weak transactions realize both of the above requirements. The restrictive nature of one copy ....

D. Barbar'a and H. Garcia-Molina. Replicated Data Management in Mobile Environments: Anything New Under the Sun? In Proceedings of the IFIP Conference on Applications in Parallel and Distributed Computing, April 1994.

....are ignorant of strict and weak transactions at other clusters. The techniques of supporting N ignorance can be incorporating in the proposed model to define d as the ignorance factor N of weak transactions. Mobile Database Systems. The effect of mobility on replication schemas is discussed in [2]. The need for the management of cached copies to be tuned according to the available bandwidth and the currency requirements of the applications is stressed. In this respect, d degree consistency and weak transactions realize both of the above requirements. The restrictive nature of one copy ....

D. Barbar'a and H. Garcia-Molina. Replicated Data Management in Mobile Environments: Anything New Under the Sun? In Proceedings of the IFIP Conference on Applications in Parallel and Distributed Computing, April 1994.

....conditions, and 4. take into account the changing locality. Although replica control schemas that address some of the above concerns have already been studied in the context of mobile file systems (for instance, see [15, 22] the database community is only starting to address these issues [4]. Our Approach. Maintaining data consistency over all distributed sites imposes unbearable overheads on mobile computing [2, 8, 11, 18] In this paper, we propose a more flexible model. Semantically related or closely located data are grouped together to form a cluster. While full consistency is ....

....the number of updates. In [23] a generalization of ESR was proposed for high level type specific operations on abstract data types. In contrast, our approach deals with low level read and write operations. Mobile Database Systems. The effect of mobility on replication schemas is discussed in [4]. The need for the management of cached copies to be tuned according to the available bandwidth and the currency requirements of the applications is stressed. In this respect, m degree consistency and weak transactions realize both of the above requirements. The restrictive nature of one copy ....

D. Barbar'a and H. GarciaMolina. Replicated Data Management in Mobile Environments: Anything New Under the Sun? In Proceedings of the IFIP Conference on Applications in Parallel and Distributed Computing, April 1994.

....of transactions that do not satisfy global serializability. The last issue we address in this section is that of data replication. The ability to replicate data in mobile environments is essential since disconnected units can continue to process objects that are stored locally. The authors in [12] point out that even though the number of copies in a system can be large, the key issue is how to manages copies that are updateable. This copies are also called the core copies and their number is likely to be small for a simple reason: it becomes too expensive to update a large number of core ....

....that it needs to change the core set, it sends the description of the new set to the referees and if a majority of them accept the change, that description becomes the new core. Referees can be highly replicated since they are only accessed when a new core is elected. As it is pointed out in [12], the directory of objects is also a replicated object that has to be managed just like any other. The authors conclude that standard techniques to manage copies are also adequate to manage the directory. However, a variation of the primary copy algorithm, called Primary by Row is proposed to ....

# D. Barbar and H. Garcia-Molina, "Replicated Data Management in Mobile Environments: Anything New Under the Sun?" Proc. IFIP WG10.3 Working Conf. Applications in Parallel and Distributed Computing, Caracas, Venezuela, Apr. 1994.

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Daniel Barbará, Hector Garcia-Molina: "Replicated Data Management in Mobile Environments: Anything New Under the Sun?", IFIP Transactions A, Vol. A-44, pp. 237-246, April 1994.

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