Topics of the Lesson:
• Introduction of Database
• File-based systems
• Database management systems
• Comparison between File-based system and Database management systems
Functions of DBMS
Introducing Database:
The simplest definition is given by Date (1999, p. 2) according to which Database is a
collection of computerized data files. In simple words it is computerized
record keeping.
Examples of Database Applications
• Purchases from the supermarket
• Purchases using your credit card
• Booking a holiday at the travel agents
• Using the local library
• Taking out insurance
• Using the Internet
• Studying at university
File-based Systems
• Collection of application programs that perform services for the end users (e.g. reports).
• Each program defines and manages its own data
• E.g. is a C++ system that accepts and stores data. In such case the sequence in which the fields are recorded is coded in the program, not in the file.
Limitations of File-Based Approach
• Separation and isolation of data
– Each program maintains its own set of data.
– Users of one program may be unaware of potentially useful data held by other programs.
– Duplication of data
– Same data is held by different programs.
– Wasted space and potentially different values and/or different formats for the same item.
• Duplication of data
– Same data is held by different programs.
– Wasted space and potentially different values and/or different formats for the same item.
Database Approach
• Arose because:
– Definition of data was embedded in application programs, rather than being stored separately and independently.
– No control over access and manipulation of data beyond that imposed by application programs.
•
Result:
– the database and Database Management System (DBMS).
Formal definition of Database
• Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization.
• System catalog (metadata) provides description of data to enable program–data independence.
• Logically related data comprises entities, attributes, and relationships of an organization’s
information.
Database Management System (DBMS)
• A software system that enables users to define, create, and maintain the database and that provides controlled access to this database.
Views
• Allows each user to have his or her own view of the database.
• A view is essentially some subset of the database.
Functions of Database Management System
· Provide Security
· Data Integrity
· Provide controlled concurrency
· Reduced data redundancy
· Crash Recovery
· Backup and Recovery
