DBMS Architecture

                   

DBMS Architecture

Handwritten Notes- Click Here

DBMS Architecture describes the structure of a database system and explains how users, applications, and database components interact with stored data.


DBMS architecture can be studied in two major parts:

1.Three-Schema Architecture – explains the logical structure of the database.
2.Functional Components – explains how the DBMS software processes user requests.

1. Three-Schema Architecture
  • The main purpose of the three-schema architecture is to provide users with an abstract view of data.
  • It hides unnecessary details about how the data is physically stored and helps achieve data independence.
The three Levels are:
  1. External Level
  2. Conceptual Level
  3. Internal Level


1. External Level (View Level)
  • The external level is the highest level of the DBMS architecture. It represents the way individual users view the database.
  • It provides separate database views according to the requirements of different users.
Example:
A student may be allowed to view only their marks.
An administrator may be able to view information about all students. 


B. Conceptual Level (Logical Level)

The conceptual level describes the complete logical structure of the database and the relationships between the data.

It defines:

  • Entities
  • Attributes
  • Relationships
  • Constraints

The conceptual level does not describe how the data is physically stored on storage devices.


3. Internal Level (Physical Level)

The internal level is the lowest level of DBMS architecture. It describes how data is actually stored in physical storage.

It deals with storage-related details such as:

  • File organization
  • Data compression
  • Hashing
  • Record arrangement
  • Storage allocation


2. Functional Components of DBMS

Functional components explain how the DBMS software processes queries and manages stored data.

The major components are:

  1. Query Processor
  2. Storage Manager

A. Query Processor
The query processor handles database queries and converts them into operations that can be executed by the DBMS


1. DDL Interpreter
The DDL Interpreter processes Data Definition Language (DDL) commands such as:
  • CREATE
  • ALTER
  • DROP

2. DML Compiler
The DML Compiler processes Data Manipulation Language (DML) statements such as:
  • SELECT
  • INSERT
  • UPDATE
  • DELETE

3. Query Optimizer

The Query Optimizer determines an efficient way to execute a query.

4. Query Evaluation Engine
The Query Evaluation Engine executes the low-level instructions generated by the query processing components.



B. Storage Manager
The Storage Manager acts as an interface between the low-level data stored in the database and the application programs.

1. Authorization and Integrity Manager

  • Checks whether a user has permission to access particular data.
  • Helps enforce integrity constraints.
  • Prevents unauthorized access to database information. 
2. Transaction Manager
The Transaction Manager manages database transactions.

It helps maintain the database in a consistent state even when:

  • System failures occur.
  • Multiple transactions execute concurrently. 
3. Buffer Manager
  • The Buffer Manager transfers required data between disk storage and main memory (RAM).
  • It manages the temporary storage area used while database operations are being performed.
4. File Manager
  • The File Manager manages the allocation of storage space on the disk.
  • It also manages the data structures used for representing information stored in the database.



Data Structures Used by the DBMS
The storage system maintains different types of information required for database operations.

1. Data Files
Data files contain the actual database data.

2. Data Dictionary
The data dictionary stores information about the database, such as schema-related information

3. Indices
Indexes are used to provide faster access to data.

4. Transaction Logs
Transaction logs record changes made to the database.They are useful for recovery when a system failure or crash occurs.


Video Explanation



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