Issues: Distributed DBMS (DDBMS)

A distributed database management system (DDBMS) is where the database of an organisation is stored in many places, and made available via a variety of communications networks.

A database or databases that is/are located in a place or places other than where the user is located. Hard disks are connected by a communications network.

• Distributed DBMS should be considered when
  • Most of the processing is local, but consolidation is required.
• The DDBMS coordinates access to data at various nodes
  • Determines the location from which to retrieve data
  • Provides data management (security, concurrency, recovery)
• Examples
  • Databases may be maintained in regional offices and head office, or even overseas.
  • Police, Ambulance have distributed databases centralised on regions, where a local knowledge by operators is important, each site can be backed up onto another such as in the case of a natural disaster.
  • Large department stores would be candidates for distributed databases, since the majority of the transactions would be generated "in-store" with management enquiries consolidating this data across all stores.
• Advantages
  • Increased reliability and availability
  • Local control
  • Modular (incremental) growth
  • Lower communication costs
  • Faster response
• Disadvantages
  • Software cost and complexity
  • Processing overheads
  • Data integrity
  • Slower response

Ref: Mcfadden, Hoffer, Prescott (1999) pp 421-422
[Rev 23/06/99] 30/4/97 © 1997-99 V/2-Com (Verhaart), P O Box 8415, Havelock North, New Zealand.