1. Distributed database system
Chapter 1
Distributed database system

2. Introduction to DDS Database Distributed database
A database is a collection of information that is organized so that it can easily be accessed, managed, and updated.
Distributed database
A distributed database is a database in which portions of the database are stored on multiple computers within a network. Users have access to the portion of the database at their location so that they can access the data relevant to their tasks without interfering with the work of others.

3. Distributed Database System
DBMS
data
DBMS
data
DBMS
data
DBMS

4. DISTRIBUTED DATABASE ARCHITECTUR
CLIENT
CLIENT
CLIENT
CLIENT
CLIENT
CLIENT
LAN
DBMS
DBMS
CLIENT
CLIENT
CLIENT
WIDE AREA NETWORK
KABUL
NANGAR HAR
WIDE AREA NETWORK
CLIENT
CLIENT
CLIENT
CLIENT
CLIENT
LAN
DBMS
DBMS
CLIENT
CLIENT
CLIENT
CLIENT
HARAAT
KHOST

5. DDBMS
A DDBMS (distributed database management system) is a centralized application that manages a distributed database as if it were all stored on the same computer.

6. COMPONENTS OF A DDBMS Computer Network Site 1 DDBMS DC LDBMS GSC DB
LDBMS = Local DBMS
DC = Data Communications GSC = Global Systems Catalog DDBMS = Distributed DBMS
DDBMS DC
Site 2

7. Distributed Database Architecture
Classification of DDBMS
Homogenous Distributed Database Systems
A homogenous distributed database system is a network of two or more Oracle Databases that reside on one or more machines.

8. Homogenous Distributed Database Systems

9. Heterogeneous Distributed Database Systems
Different sites may use different schemas and software
Difference in schema is a major problem for query processing
Difference in software is a major problem for transaction processing
Sites may not be aware of each other and may provide only limited facilities for cooperation in transaction processing.

10. ADVANTAGES Reduced Communication Overhead Improved Processing Power
Most data access is local, less expensive and performs better.
Improved Processing Power
Instead of one server handling the full database, we now have a collection of machines handling the same database.
Removal of Reliance on a Central Site
If a server fails, then the only part of the system that is affected is the relevant local site. The rest of the system remains functional and available.

11. ADVANTAGES
Expandability
It is easier to accommodate increasing the size of the global (logical) database.
Local autonomy
The database is brought nearer to its users. This can effect a cultural change as it allows potentially greater control over local data .

12. Distributed Data Processing (DDP)
Arrangement of networked computers in which data processing capabilities are spread across the network. In DDP, specific jobs are performed by specialized computers which may be far removed from the user and/or from other such computers. This arrangement is in different to 'centralized' computing in which several client computers share the same server (usually a mini or mainframe computer) or a cluster of servers. DDP provides greater scalability, but also requires more network administration resources.

13. CLIENT/SERVER DATABASE SYSTEM
Client Process
Manages user interface Accepts user data Processes application
Generates database requests (SQL)
Transmits database requests to server
Receives results from server
Formats results according to application logic
Present results to the user

14. CLIENT/SERVER DATABASE SYSTEM
Server Process
Accepts database requests
Processes database requests
Performs integrity checks
Handles concurrent access
Optimises queries
Performs security checks
Enacts recovery routines
Transmits result of database request to client

15. NETWORK DBMS  SERVER      DATA LOGIC PRESENTATION LOGIC
CLIENT#1
CLIENT#2
CLIENT#3
CLIENT/SERVER
DBMS ARCHITECTURE 
NETWORK
SERVER 
D/BASE 
DBMS   
DATA LOGIC
PRESENTATION LOGIC
 Data Request
 Data Response

16. C.J. Date's 12 Distributed DBMS Rules.
Local Autonomy
The sites in a distributed system should be autonomous or independent of each other.
No Reliance on Central Site
A distributed database system should not rely on a central site, because a single central site may become a single point of failure, affecting the entire system. Also, a central site may become affecting the distributed system's performance.

17. C.J. Date's 12 Distributed DBMS Rules.
Continuous Operation
A distributed database system should never require downtime.
Location Transparency and Location Independence
Users and/or applications should not know, where the data is physically stored; instead, users and/or applications should behave as if all data was stored locally.

18. C.J. Date's 12 Distributed DBMS Rules.
Fragmentation Independence
Relational tables in a distributed database system can be divided into fragments and stored at different sites transparent to the users and applications.
Replication Independence
Data can be transparently replicated on multiple computer systems across a network.
Distributed Query Processing
The performance of a given query should be independent of the site at which the query is submitted.

19. C.J. Date's 12 Distributed DBMS Rules.
Distributed Transaction Management
A distributed system should be able to support automatic transactions.
Hardware Independence
A distributed database system should be able to operate and access data spread across a wide variety of hardware platforms.
Operating System Independence
A distributed database system should be able to run on different operating systems.

20. C.J. Date's 12 Distributed DBMS Rules.
Network Independence
A distributed database system should be designed to run regardless of the communication protocols and network topology used to interconnect various system nodes.
DBMS Independence
An ideal distributed database management system must be able to support interoperability means able to exchange and use information between DBMS systems running on different nodes, even if these DBMS systems are unlike (heterogeneous).