World Library  
Flag as Inappropriate
Email this Article

Data synchronization

Article Id: WHEBN0007360695
Reproduction Date:

Title: Data synchronization  
Author: World Heritage Encyclopedia
Language: English
Subject: SyncML, OfflineIMAP, Post-PC era, SQL Anywhere, Comparison of notetaking software
Collection: Data Synchronization, Fault-Tolerant Computer Systems
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Data synchronization

Data synchronization is the process of establishing consistency among data from a source to a target data storage and vice versa and the continuous harmonization of the data over time. It is fundamental to a wide variety of applications, including file synchronization and mobile device synchronization e.g., for PDAs.[1]

Contents

  • File-based solutions 1
  • Theoretical models 2
    • Unordered data 2.1
    • Ordered data 2.2
  • See also 3
  • Notes 4

File-based solutions

There are tools available for file synchronization, version control (CVS, Subversion, etc.), distributed filesystems (Coda, etc.), and mirroring (rsync, etc.), in that all these attempt to keep sets of files synchronized. However, only version control and file synchronization tools can deal with modifications to more than one copy of the files.

  • File synchronization is commonly used for home backups on external hard drives or updating for transport on USB flash drives. The automatic process prevents copying already identical files, thus can save considerable time relative to a manual copy, also being faster and less error prone.[2]
  • Version control tools are intended to deal with situations where more than one user attempts to simultaneously modify the same file, while file synchronizers are optimized for situations where only one copy of the file will be edited at a time. For this reason, although version control tools can be used for file synchronization, dedicated programs require less overhead.
  • Distributed filesystems may also be seen as ensuring multiple versions of a file are synchronized. This normally requires that the devices storing the files are always connected, but some distributed file systems like Coda allow disconnected operation followed by reconciliation. The merging facilities of a distributed file system are typically more limited than those of a version control system because most file systems do not keep a version graph.
  • Mirror (computing): A mirror is an exact copy of a data set. On the Internet, a mirror site is an exact copy of another Internet site. Mirror sites are most commonly used to provide multiple sources of the same information, and are of particular value as a way of providing reliable access to large downloads.

Synchronization can also be useful in encryption for synchronizing Public Key Servers.[3]

Theoretical models

Several theoretical models of data synchronization exist in the research literature, and the problem is also related to the problem of Slepian–Wolf coding in information theory. The models are classified based on how they consider the data to be synchronized.

Unordered data

The problem of synchronizing unordered data (also known as the set reconciliation problem) is modeled as an attempt to compute the symmetric difference S_A \oplus S_B = (S_A - S_B) \cup (S_B - S_A) between two remote sets S_A and S_B of b-bit numbers.[4] Some solutions to this problem are typified by:

Wholesale transfer
In this case all data is transferred to one host for a local comparison.
Timestamp synchronization
In this case all changes to the data are marked with timestamps. Synchronization proceeds by transferring all data with a timestamp later than the previous synchronization.[5]
Mathematical synchronization
In this case data are treated as mathematical objects and synchronization corresponds to a mathematical process.[4][6][7]

Ordered data

In this case, two remote strings \sigma_A and \sigma_B need to be reconciled. Typically, it is assumed that these strings differ by up to a fixed number of edits (i.e. character insertions, deletions, or modifications). Then data synchronization is the process of reducing edit distance between \sigma_A and \sigma_B, up to the ideal distance of zero. This is applied in all filesystem based synchronizations (where the data is ordered). Many practical applications of this are discussed or referenced above.

It is sometimes possible to transform the problem to one of unordered data through a process known as shingling (splitting the strings into shingles).[8]

See also

Notes

  1. ^ Agarwal, S.; Starobinski, D.;  
  2. ^  
  3. ^ sks.dnsalias.net
  4. ^ a b Minsky, Y.;  
  5. ^ Palm developer knowledgebase manuals
  6. ^  
  7. ^ Y. Minsky and A. Trachtenberg, Scalable set reconciliation, Allerton Conference on Communication, Control, and Computing, Oct. 2002
  8. ^ S. Agarwal; V. Chauhan;  
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.