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DISTRIBUTED DATABASE

DISTRIBUTED DATABASE. Centralized & Distributed Database. Single site database – centralized database A database is located at a single site or distributed over several sites Multi-site database – distributed database A database is stored on multiple computers (not connected).

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DISTRIBUTED DATABASE

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  1. DISTRIBUTED DATABASE

  2. Centralized & Distributed Database • Single site database – centralized database • A database is located at a single site or distributed over several sites • Multi-site database – distributed database • A database is stored on multiple computers (not connected)

  3. Centralised DB – DB located at single site or location Dumb Terminal Central Computer DB Dumb Terminal Remote Terminal

  4. Distributed DB – DB distributed over several sites DBMS 1 DBMS 3 Network DBMS 2

  5. Disadvantages of centralized database Performance degradation High cost Fast access Reliability issues Advantages of distributed database Reduced cost High availability Support graphical interfaces Shared workload Centralized & Distributed Database

  6. Data Distribution Strategies • Data allocation or distribution – a process of deciding where to locate the data • Three strategies • Centralized – at a single site • Partitioned – split the database • Replication – duplicates the database

  7. Data Replication • Two types of replication : • Fully replicated – same data store at several site • Partially replicated – part of database at one site

  8. Data Replication • Advantages : • Fast response • Reduced transmission cost • High reliability • Disadvantages : • Increased storage requirement • Increased cost • Reduced security

  9. Partitioning • Two types of partitioning i. Horizontal partitioning – rows of table are distributed • Advantages : • Fast access • Reduced cost • Security • Disadvantages : • Backup problem • Varying access speed Row 1 and 2 are split from the original table and located in different location

  10. Partitioning ii. Vertical partitioning – columns of table are distributed • Advantages : • Fast access • Reduced cost • security • Disadvantages : • Backup problem • Speed difference Column 1 and 2 are split from the original table and located in different location

  11. Distributed DBMS • Distributed processing for distributed database • Must provide the following transparencies : • Transaction transparency? • Distribution transparency? • Failure transparency? • Performance transparency? • Heterogeneity transparency?

  12. Client/server is normally a 2-tier architecture • Tier-1 : Client • Tier-2 : DB server • More complex client/server or web-based systems may require 3-tier architecture • Tier 1 : Client • Tier 2 : Application server • Tier 3 : DB server

  13. ODBC Standard • Is an interface by which application programs can access and process SQL databases in a DBMS-independent manner • Any application that uses the ODBC interface will be able to access any other DB without changing the program coding • If you have an application program that uses ODBC interface, you should be able to access an Oracle, Informix, Access or other DB.

  14. END

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