Basics of Database System & DBMS

The DBMS is an interface between DB and users.
User<---->DBMS<---->OS<---->Database.
Database System vs File System
Disadv of file system includes-
1. Dependency of file system on program and vice-versa.
2. Data Redundancy- same piece of data may be stored at more than one place or file.
3. Difficulty in accessing data
4. Data Isolation- data issolated in different file system, may not be retrieved by other programs.
5. Data Integrity issue-
6. Atomicity Problem- It is crucial that whenever a failure occurs, data be restored at consistent state that existed prior to the failure. It is difficult to ensure atomicity on conventional file system.
7. Security Problem- Not much security option is available for conventional file system.

Database system and DBMS overcomes all the above limitations and also allows data abstraction. Data abstraction can be done on physical, logical and view level.

Database Instance- The collection of information at any given point in time is called instance of the database.
The overall design of a database is called Database Schema. Each database may have several schemas that are partitioned according to the level of abstration.
Data Models-It is defined as the structure of the database. It is collection of conceptual tools like for describing data, data relationships, data semantics and consistancy constraints.
Type of data models:
ER Model(Entity relationship), Relational model, object oriented, network data model are few to name.
Database users and administrators-
Users type are naive, application programmers, sophisticated users and specialized user.
Sophisticated users interacts with system without writing application programs. Specialized users are sophisticated users who write specialized DB program that do no fit into tradional data processing framework.
Roles of DBA:
Schema definition, Storage structure and access method definition, Granting of authorization for for data access and Routine management like regular DB backup, ensuring enough free space, monitoring jobs running and ensuring the performance of the database.

Transaction Management:
Transaction management forms the main component of DBMS since each and every query is considered to be a transaction.