Download DDS Chapter 1

Chapter 1
DISTRIBUTED DATABASE SYSTEM
Introduction to DDS
 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.
Distributed Database System
Distributed Database System
DBMS
DBMS
DBMS
DBMS
data
data
data
data
DISTRIBUTED DATABASE ARCHITECTUR
CLIENT
CLIENT
CLIENT
CLIENT
CLIENT
CLIENT
CLIENT
DBMS
DBMS
LAN
CLIENT
NANGAR HAR
KABUL
CLIENT
CLIENT
CLIENT
CLIENT
CLIENT
LAN
CLIENT
CLIENT
CLIENT
DBMS
DBMS
HARAAT
CLIENT
CLIENT
KHOST
 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.
COMPONENTS OF A DDBMS
Site 1
DDBMS
DC LDBMS
GSC
GSC
Computer
Network
DDBMS
DC
Site 2
DB
LDBMS = Local DBMS
DC = Data Communications
GSC = Global Systems Catalog
DDBMS = Distributed DBMS
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.

Homogenous Distributed Database Systems
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.

ADVANTAGES
• Reduced Communication Overhead
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.
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 .
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.
CLIENT/SERVER DATABASE SYSTEM
 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
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
CLIENT
#1

CLIENT/SERVER
DBMS ARCHITECTURE
SERVER
CLIENT
#2


D/BASE

CLIENT
#3


DATA LOGIC
PRESENTATION LOGIC
 Data Request
 Data Response
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.
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.
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.
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.
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).