Download Database Concepts

DISTRIBUTED DATABASES
AND DDBMS
Learning Objectives



Describe various DDBMS implementations
Explain how database design affects the DDBMS
environment
Apply DDBMS principles to solve problems
Definitions

Distributed Database: A single logical
database that is spread physically across
computers in multiple locations that are connected
by a data communications link

Decentralized Database: A collection of
independent databases on non-networked
computers
They are not the same thing!
Distributed database environments (adapted from Bell and Grimson,
1992)
Homogeneous Database
Identical DBMSs
Source: adapted from Bell and Grimson, 1992.
Typical Heterogeneous Environment
Non-identical DBMSs
Source: adapted from Bell and Grimson, 1992.
Example of Replication
CRM Db
User’s View of Db
•Customers
•Sales Staff
•Orders
Actual Implementation
N. America
Europe
•All Customers
•All Sales Staff
•All Orders
•All Customers
•All Sales Staff
•All Orders
Master
Replica
Example of Horizontal Partitioning
CRM Db
User’s View of Db
•Customers
•Sales Staff
•Orders
Actual Implementation
N. America
Europe
•NA Customers
•NA Sales Staff
•NA Orders
•E Customers
•E Sales Staff
•E Orders
Example of Vertical Partitioning
ERP System
User’s View of Db
•Financials
•Customer Service
•Prod. Support
•Human Resources
Actual Implementation
N. America
•Financials
•Human Resources
Europe
•Customer Service
•Prod Support
Five Distributed Database
Organizations
 Centralized database, distributed access
 Replication with periodic snapshot update
 Replication with near real-time synchronization of
updates
 Partitioned, one logical database
 Partitioned, independent, nonintegrated segments
Distributed Design Strategies
Distributed DBMS: Transparency

Location Transparency


Replication Transparency


User/application does not need to know where data resides
User/application does not need to know about duplication
Failure Transparency

Either all or none of the actions of a transaction are committed
Applying the
concepts through examples:


Client server: Mono, 2-tier, 3-tier, n-tier?
Single Site / Multi Site data? Y/N
 If



multi-site: Partitioned H/V or Replicated?
Location Transparency: Y/N?
Replication Transparency: Y/N?
Failure Transparency: Y/N?
Distributed DBMS architecture
Local Transaction Steps
1.
2.
3.
4.
5.
Application makes request to distributed DBMS
Distributed DBMS checks distributed data
repository for location of data. Finds that it is
local
Distributed DBMS sends request to local DBMS
Local DBMS processes request
Local DBMS sends results to application
Distributed DBMS Architecture - cont.
Showing local transaction steps
2
1
3
5
4
Local transaction – all
data stored locally
Global Transaction Steps
1.
2.
3.
4.
5.
6.
7.
8.
Application makes request to distributed DBMS
Distributed DBMS checks distributed data repository for
location of data. Finds that it is remote
Distributed DBMS routes request to remote site
Distributed DBMS at remote site translates request for its local
DBMS if necessary, and sends request to local DBMS
Local DBMS at remote site processes request
Local DBMS at remote site sends results to distributed DBMS
at remote site
Remote distributed DBMS sends results back to originating
site
Distributed DBMS at originating site sends results to
application
Distributed DBMS architecture – cont
Showing global transaction steps
2
3
1
7
8
6
4
5
Global transaction – some
data is at remote site(s)
DISTRIBUTED DATABASE AND DDBMS
Questions?