Data Independence in DBMS:
Upper level are unaffected by changes in lower level.
Two Types of Data Independence:
a)Physical Data Independence:
- Physical storage structure or devices can be changed without affecting conceptual schema.
- Modification done to improve performance.
- It provide independence to conceptual schema and external schema
b)Logical Data Independence:
- Conceptual schema can be changed without affecting external schema.
- Structure of database is altered when modification done in conceptual schema.
- It provide independence to external schema.
- Processor/main memory(used for execution)
- Secondary Storage devices(for physical storage)
5)Procedures(Set of rules for database management)
Types of Users:
End Users of the database who work through menu driven application programs, where the type and range of response is always indicated to the users.
Those users who may communicate with database directly through an online terminal.
Those users who are responsible for developing the application program.
DBA directs or performs all activities related to maintaining a successful database environment.
Function of DBA:
- Defining Conceptual Schema
- Physical Database Design
- Tuning database performance
- Security and Integrity Check
- Back up and Recovery Strategies
- Improving query processing performance
- Granting User Access
1)DDL(Data Definition Language):
- Deals with database schemas and description, how the data should reside in the database.
- Used to alter/modify a database or table structure and schema.
Command used in DDL:
2)DML(Data Manipulation Language)
- Deals with data manipulation
- These statements afffects records in a table.
Command used in DML:
- Lock Table
Two Types of DML:
a)Procedural DML(How data is fetch)
b)Non-Procedural DML(What data is to be fetch)
3)DCL(Data Control Language)
Control the level of access that users have on database objects.
Command used in DCL:
Control and manage transactions to maintain integrity of data within SQL statement.
Command used in Transaction Language:
- Set Transaction