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Chapter 9 : Distributed Database.

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Presentation on theme: "Chapter 9 : Distributed Database."— Presentation transcript:

1 Chapter 9 : Distributed Database

2 Chapter 9 - Objectives Concepts.
Advantages and disadvantages of distributed databases. Functions and architecture for a DDBMS. Comparison criteria for DDBMSs.

3 Concepts Distributed Database
A logically interrelated collection of shared data (and a description of this data), physically distributed over a computer network. Distributed DBMS Software system that permits the management of the distributed database and makes the distribution transparent to users.

4 Centralized & Distributed Database
Single site database – centralized database A database is located at a single site Multi-site database – distributed database A database is stored on multiple computers (not connected)

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

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

7 Centralized & Distributed Database
Ad/Disadvantages of centralized database Performance degradation (no. of users) High cost (when no. of access , communication transmission cost Fast access as all at one site (advantage) Reliability issues (if one fails, all process stop)

8 Centralized & Distributed Database
Advantages of distributed database Reduced cost – data needed at the local site, so reduce cost High availability – if one site fails, data can be still accessed from other sites Support graphical interfaces – more user friendly interfaces Shared workload – spread over several sites

9 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 (vertical/horizontal) Replication – duplicates the database/copy

10 Data Replication Two types of replication :
Fully replicated – same data store at several site Partially replicated – part of database at another site

11 Data Replication Advantages (available locally) :
Fast response (queries processed faster) Reduced transmission cost (DB close to user) High reliability (got copies) Disadvantages (duplicate/redundant data): Increased storage requirement Increased cost (changes/update must be done to all the DB) Reduced security (poor security at one site, allows attacks to all the data in DB)

12 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 Student_ID Student_Name Age A1 Ali 22 A2 Siti 46 A3 Raju 44 A4 Karen 21 Row 1 and 2 are split from the original table and located in different location

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

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

15 Transaction transparency?
Transaction maintains consistency and the transaction completed entirely or it is aborted Distribution transparency? Gives an impression to user that there is only one DB when in actual fact it is split and scattered at several sites Failure transparency? if any site fails, it is not known by other users at other sites, their transaction goes on as usual

16 Performance transparency?
The overall performance of the DDBMS is not significantly different from the centralized DB Heterogeneity transparency? Gives an impression that there is only one DBMS being used when in actual fact there are several DBMS being used

17 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

18 ODBC (Open DB Connectivity) 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.

19 END

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