DBMS

2. Lecture 2 DDMS Definition
•Collection of logically inter related databases
•Spread physically across multiple locations
•Connected by a data communication link.

3. Main characteristics
• Solution that has been adopted for a single
organization.
• Develop a database system for its requirements
• Analyst(s) analyze the requirements
• like, client-server, desktop based, or distributed
database

4. Major characteristics of a DDBS
• Data management at multiple sites
• Local requirements
local Sites
Local User
• Global perspective
local requirements
global requirements
central management requirements

5. •DDBS fulfils the global requirements
•data for these requirements is fetched from all
the local sites
•fetching and merging is hidden from the
global user

6. DDBS environment types of accesses
• Local access: the access by the users connected to a site
and accessing the data from the same site.
• Remote access: a user connected to a site, lets say site 1,
and accessing the data from site 2.
• Global access: no matter from where ever the access is
made, data will be displayed after being collected from all
locations

7. Distributed databases; where to apply
The candidate applications for a DDBS have following two main
characteristics:
• 1- Large number of users
• 2- Users are physically spread across large geographical area
Banking Applications
Air ticketing
Business at multiple locations

8. Distributed Database Management System
• DBMS for a centralized or client-server database
• like a normal DBMS on the local site,
• Provides is the creation and maintenance of the global access
• Data across multiple sites is accessed against a single query
• Current commercial DBMS vendors (like Oracle, SQL Server,
DB2, Sybase)
• Provide different versions for different situations
• Desktop database for the single computer usage
• Client-server database

9. Decentralized database
• A collection of Independent databases on non-networked
computers
• Data at multiple computers is related
• Computers are not linked
• Data has to be accessed from multiple computers
• Transferring data across these computers