DBMS Features (Cambridge International A-Level Computer Science)
DBMS vs file-based systems
What is a DBMS?
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A DBMS (Database Management System) is software that is used to create, manage, and interact with databases
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A DBMS provides several key features, including:
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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
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Provides data security and access control to keep data safe
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Maintains data integrity by enforcing rules and constraints, e.g.
- If the data is changed in one place it is updated in every other place
- Ensures each foreign key has a corresponding primary key
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Supports concurrency control so multiple users can access the database at the same time without errors
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Ensures data independence so changes to storage methods do not affect how data is used
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Offers backup and recovery tools to protect against data loss
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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 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
Worked Example State what is meant by a data dictionary and give one example of an item typically found in a data dictionary. [2]
Final answer: 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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