DBMS Structure
The structure of a Database Management System (DBMS) can be referred to in two ways:
Internal Structure: This refers to the functional components that make up the DBMS software and how they interact with each other.
Three-Schema Architecture: This is a logical view of how data is organized within the DBMS, focusing on different user perspectives.
Internal Structure
Database Management System (DBMS) is software that allows access to data stored in a database and provides an easy and effective method of defining, storing, manipulating, protecting the data.
The database system is divided into three components: Query Processor, Storage Manager, and Disk Storage.
Query Processor:
Receives user queries (often written in SQL) and translates them into instructions the database system understands. It then manages the execution of those instructions, retrieving and manipulating data as needed.
Query Processor contains the following components –
DML Compiler: It processes the DML statements into low level instruction (machine language), so that they can be executed.
DDL Interpreter: It processes the DDL statements into a set of table containing meta data (data about data).
Embedded DML Pre-compiler: It processes DML statements embedded in an application program into procedural calls.
Query Optimizer: It executes the instruction generated by DML Compiler.
Storage Manager:
Handles the physical storage and retrieval of data. It interacts with the operating system and disk storage to efficiently store, organize, and access data on physical media.
It contains the following components –
Authorization Manager: It ensures role-based access control, i.e,. checks whether the particular person is privileged to perform the requested operation or not.
Integrity Manager: It checks the integrity constraints when the database is modified.
Transaction Manager: It controls concurrent access by performing the operations in a scheduled way that it receives the transaction. Thus, it ensures that the database remains in the consistent state before and after the execution of a transaction.
File Manager: It manages the file space and the data structure used to represent information in the database.
Buffer Manager: It is responsible for cache memory and the transfer of data between the secondary storage and main memory.
Disk Storage:
This is the physical storage device (hard drive, solid-state drive) where the database files reside. The Storage Manager interacts with the disk to read and write data as instructed.
It contains the following components –
Data Files: It stores the data.
Data Dictionary: It contains the information about the structure of any database object. It is the repository of information that governs the metadata.
Indices: It provides faster retrieval of data item.
Three-Schema Architecture
This is a conceptual framework that describes data organization at different levels within a DBMS:
Internal Schema (Physical Schema): The lowest level, defines how data is physically stored and accessed by the DBMS. It is responsible for storing and retrieving data from the storage devices, such as hard drives or solid-state drives. It deals with low-level implementation details such as data compression, indexing, and storage allocation.
Conceptual Schema (Logical Schema): Represents the logical structure of the data as seen by database administrators and application developers. It focuses on data entities (tables), attributes (columns), and the relationships between them. This schema provides a blueprint for the database's logical organization.
External Schema (View): The highest level, caters to specific user needs. It defines different views of the data relevant to a particular user group or application. Views can simplify complex structures or hide irrelevant data, providing a customized view for each user.
The three levels are connected through a schema mapping process that translates data from one level to another. The schema mapping process ensures that changes made at one level are reflected in the other levels.
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