Database Management System (DBMS)

What is a Database?

• A database is any collection of related data.

• A database is a persistent, logically coherent collection of inherently meaningful data, relevant to some aspects of the real world.

What is a Database Management System?

A database management system (DBMS) is a collection of programs that enables users to create and maintain a database. According to the ANSI/SPARC DBMS Report (1977), a DBMS should be envisioned as a multi-layered system:

Function of DBMS:

The main functions of operating systems are as follows:

Process Management: As a process manager, the OS handles the creation and deletion of processes, suspension and resumption of processes and scheduling and synchronisation of processes.

Memory Management: As a memory manager, the OS handles allocation and reallocation of memory space as required by various programs.

File Management: The OS is responsible for creation and deletion of files and directories. It also take care of other file- related activities such as organising, storing, retrieving, naming and protecting the files.

Device Management: OS provides input/output subsystem between process and device driver. It handles the device cache, buffers and interrupts. OS also detects device failure and notifies the same to the user.

Security Management: The OS protects system resources and information against destruction and unauthorized use.

User Interface: OS provides the interface between the user and the hardware . The user interface is the layer that actually interacts with the computer operator. The interface consists of a set of commands or menus through which a user communicates with a program.

Various Levels of DBMS:

A DBMS is implemented through three general Levels:

External Level: This is the level closet to the users and is concerned with the way in which the data are viewed by individual users. For example, even though the bank database sores a lot much information, an account holder (a user) is interested only in his account details and not with the rest of information stored in the database. 

Conceptual Level:  This level of abstraction describes what data are actually stored in the database. It also describes the relationships existing among data.

Internal Level:  This is the closest to physical storage. This level is also sometimes termed as physical level. It describes how the data are actually stored on the storage medium.