dbms-features

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DBMS vs file-based systems

A DBMS (Database Management System) is software that is used to create, manage, and interact with databases
A DBMS provides several key features, including:
- Defines a logical schema – the overall logical design of the database (tables, fields, relationships, and constraints), showing how data is organised independently of how it is physically stored
- Provides data security and access control to keep data safe
- Maintains data integrity by enforcing rules and constraints
- Supports concurrency control so multiple users can access the database at the same time without errors
- Ensures data independence so changes to storage methods do not affect how data is used
- Offers backup and recovery tools to protect against data loss
It addresses the limitations of file-based systems by:

Area	Limitation in file-based systems	How a DBMS solves it
Data redundancy	Same data is stored in multiple files, wasting space and causing confusion	A DBMS centralises data, so it is stored once and referenced when needed
Data inconsistency	Data may differ between files if one is updated but others are not	A DBMS ensures data consistency by updating a single source of truth
Data management	Each application stores and manages its own data	A DBMS provides a data dictionary that defines all data elements across the system (field/table names, data types)
Data modelling	No structured way to represent or link data	A DBMS uses data modelling tools (e.g. ER diagrams) to define entities and relationships
Logical schema	The overall logical design of the database (tables, fields, relationships, and constraints)	Shows how data is organised and used, independently of how it is physically stored
Data integrity	Difficult to enforce validation rules across different files	A DBMS uses constraints (e.g. primary keys, foreign keys) to enforce integrity
Data security	Poor control over who can access or change data	A DBMS supports user accounts, access rights, and permissions for individuals/groups
Backup procedures	Often manual and inconsistent	A DBMS includes automated backup and recovery tools to reduce risk of data loss

The developer interface allows developers to write database queries using Structured Query Language (SQL)
This is more flexible than using query-by-example tools, which are visual and simplified
Using SQL allows the developer to create more complex and precise queries to search, update, or manage data

Component	Function
DDL interpreter	Interprets Data Definition Language (DDL) commands like `CREATE`, `ALTER`, and `DROP` and updates the data dictionary
DML compiler	Compiles Data Manipulation Language (DML) statements (e.g. `SELECT`, `INSERT`, `UPDATE`) into low-level instructions and optimises the query
Query evaluation engine	Executes the compiled instructions to retrieve or manipulate the actual data in the database

Together, these components make sure that any query written by the developer is interpreted, optimised, and executed efficiently

State what is meant by a data dictionary and give one example of an item typically found in a data dictionary. [2]

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