1. CHAPTER 25 - Distributed Databases and Client–Server Architectures
GROUP MEMBERS
Edwin Acquah
Andria Akua Abraham
Henry Cleland
Francis Asante

2. Presentation Outline Introduction and Concepts Types of DDBMS
Techniques for DDBMS Implementation
Fragmentation
Replication
Query Processing
Concurrency
Architecture

3. INTRODUCTION & CONCEPTS
DDB Technology is a merger between
Database Technology
Networks and Data Communication Technology
However, developments have been shifted from Pure DDBMS products to
Systems based on Client-Server Architectures or
Developing Technologies for accessing Distributed Heterogeneous Data sources

4. THE MAIN AIM
Decentralizing Of Processing (at the system level) while achieving an Integration of Information sources (at the logical level) within a geographically distributed systems of databases, applications and users

5. ADVANTAGES OF DISTRIBUTED DATABASES
Management of distributed data with different levels of transparency
Increased reliability and availability
Improved performance
Easier expansion

6. ADDITIONAL FUNCTIONS OF DISTRIBUTED DATABASES
Ability to keep track of the data distribution, fragmentation, and replication by expanding the DDBMS catalog.
Ability to access remote sites and transmit queries and data among the various sites via a communication network.
Executed with the proper management of the security of the data and the authorization /access privileges of users.

7. TYPES OF DISTRIBUTED DATABASES (FACTORS TO CONSIDER)
Degree of homogeneity
Degree of local autonomy

8. FEDERATED DATABASE SYSTEM
Each server is an independent and autonomous centralized DBMS.
Used when there is a global view or schema of the federation of databases that is shared by the applications.
In heterogeneous FDBS one server may be a relational DBMS, another a network DBMS and the third an object or hierarchical DBMS.

9. FEDERATED DATABASE SYSTEM ISSUES
Differences in data models
Differences in constraints
Differences in query languages

10. SEMANTIC HETEROGENEITY
The universe of discourse from which the data is drawn
Representation and meaning
The understanding, meaning and subjective interpretation of data
Transaction and policy constraints
Derivation of summaries

11. DESIGN AUTONOMY OF COMPONENT DBSs
Communication autonomy
Execution autonomy
Association autonomy.

12. Techniques for DDBMS Implementation
Fragmentation
Vertical Fragmentation (PROJECTION)
Horizontal Fragmentation (SELECT)
Mixed(Hybrid) Fragmentation
Replication
Global catalog schema
Degree of replication
Query Processing
Query Decomposition
Semijoins

13. CONCURRENCY CONTROL AND RECOVERY IN DISTRIBUTED DATABASES
Issues that arise include:
Dealing with multiple copies of data items
Failure of individual sites
Failure of communications links
Distributed commit
Distributed DEADLOCK

14. CONCURRENCY CONTROL BASED ON DISTINGUISHED COPY OF DATA ITEM
Based on an extension of centralized locking.
Idea is to designate a particular copy of each data item as a distinguished copy.
Locks for that data item deal with the distinguished copy as such all locking and unlocking requests are sent to the site that contains that copy.

15. IMPLEMENTATION OF DISTINGUISHED COPY
Primary site technique (Coordinator site)
All distinguished copies are kept on one site.
Risk and impact of failure is high
Primary Site with Backup
-Adds a backup site to curb the high risk of failure.
Primary copy technique
-distribute locks over several sites

16. 3 tier architecture Presentation layer Application layer
Database sever
Distribution transparency

17. Thank You 