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 Central Computer DB Remote Terminal Dumb Terminal

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

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

9.  Two types of partitioning i.Horizontal partitioning – rows of table are distributed  Advantages : –Fast access –Reduced cost –Security  Disadvantages : –Backup problem –Varying access speed Partitioning Student_ID Student_Na me Age A1Ali22 A2Siti46 A3Raju44 A4Karen21 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 Student_ID Student_Na me Age 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 1. Tier-1 : Client 2. Tier-2 : DB server  More complex client/server or web- based systems may require 3-tier architecture 1. Tier 1 : Client 2. Tier 2 : Application server 3. 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