DBMS Features (Cambridge (CIE) A Level Computer Science): Revision Note
Exam code: 9618
DBMS vs file-based systems
What is a DBMS?
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 |
DBMS tools
Developer interface
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
Query processor
The query processor is responsible for handling and executing SQL queries
It has several key components:
Component | Function |
|---|---|
DDL interpreter | Interprets Data Definition Language (DDL) commands like |
DML compiler | Compiles Data Manipulation Language (DML) statements (e.g. |
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
Worked Example
State what is meant by a data dictionary and give one example of an item typically found in a data dictionary. [2]
Answer
A data dictionary is data about the data structure in the database [1 mark]
Example: field name, data type, or table name [1 mark]
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