Structure Of Data Base Management System

DATA BASE MANAGEMENT SYSTEM STRUCTURE:

DBMS (Database Management System) acts as an interface between the user and the database. The user requests the DBMS to perform various operations (insert, delete, update and retrieval) on the database. The components of DBMS perform these requested operations on the database and provide necessary data to the users.

DBMS Structure is classified in to 3 parts:

1) Users

2) Data Management System

     a) Query Processor

     b) Storage Manager

3) Disk Storage

1) Users

It has 4 users

Naive Users 

Naive Users are unsophisticated users who interact with the system by using permanent application programs (e.g. automated teller machine).

Application Programmers

Application Programmers are computer professionals interacting with the system through DML calls embedded in a program written in a host language (e.g. C, PL/1, Pascal): These programs are called Application Programs. The DML Precompiled converts DML calls (prefaced by a special character like $, #, etc.) to normal procedure calls in a host language.

Sophisticated Users 

Sophisticated Users interact with the system without writing programs: They form requests by writing queries in a database query language. These are submitted to a query processor that breaks a DML statement down into instructions for the database manager module.

Database Administrator (DBA)

The DBA is a person or a group of persons who is responsible for the management of the database. The DBA is responsible for authorizing access to the database by grant and revoke permis­sions to the users, for coordinating and monitoring its use, managing backups and repairing damage due to hardware and/or software failures and for acquiring hardware and software resources as needed. In case of small organization the role of DBA is performed by a single person and in case of large organizations there is a group of DBA's who share responsibilities.

2) Date Management System

Its a combination of Query Processor & Storage Manager

Query Processor 

Embedded DML Precompiler

Embedded DML Precompiler converts DML statements embedded in an application program to normal procedure calls in the host language. The precompiler must interact with the DML compiler to generate the appropriate code.

DDL Interpreter

DDL Interpreter which interprets DDL statements and records the definitions in the data  dictionary.

DML Compiler

DML Compiler which translates DML statements in a query language into an evaluation plan consisting of low level instructions that the query evaluation engine understands.

Query Evolution Engine

Query Evolution Engine executes low-level instructions generated by the DML compiler

Storage Manager

Transaction manager

This ensures that the database remains in a constraint (correct) state despite system failures, and that concurrent transaction executions proceed without conflicting.

File manager

This manages the allocation of space on disk storage and the data structures used to represent information stored on disk.

Buffer manager

Buffer manager is responsible for fetching data from disk storage into main memory, and deciding what data to cache in memory.

3) Disk Storage

It has 4 types of storage

Data files

This stores the database itself

Data dictionary

This stores metadata about the structure of the database

Indices

This provide fast access to data items that hold particular values

Statistical data
This stores statistical information about the data in the database. This information is used by query processor to select efficient ways to execute a query