DBMS Features (Cambridge (CIE) A Level Computer Science) : Revision Note

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

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

No separation of how data is stored vs how it is used

A DBMS uses a logical schema to describe the structure independently of storage

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

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