# Databases

> CIE A-Level Computer Science · 9618
> Source: https://www.owlsprep.com/study/cie-9618-u8-overview/
> Weight: n/a

This unit covers core concepts, design, implementation and management of modern databases, a foundational topic for software development and data management, assessed in both theory and practical components of the 9618 syllabus.

**Prerequisites:** Fundamental data structures and data representation concepts

## Learning objectives

- Explain core database concepts and the value of structured data storage for real-world applications
- Design and normalise relational databases that eliminate redundancy and maintain data integrity
- Write correct Structured Query Language (SQL) statements for common database operations
- Describe advanced database architectures and mechanisms for managing concurrent multi-user access

## Unit at a glance

We start with the big picture of why databases exist, what problems they solve compared to unstructured or flat-file storage, before moving into the dominant relational database model that powers most modern applications. Next, we cover how to implement and interact with databases using Structured Query Language (SQL), the global standard for relational data work.

We then cover the critical process of database normalisation to eliminate data redundancy and protect data integrity, before moving to advanced topics including distributed database architectures and transaction management for multi-user systems. Each topic builds incrementally on the previous one, moving from core concepts to practical design and advanced system management.

This unit is split into the following linked sub-topics:
- [Database concepts](https://www.owlsprep.com/study/cie-9618-u8-database-concepts/) — Introduces core terminology, the limitations of flat files, and the purpose of modern database systems.
- [Relational database model](https://www.owlsprep.com/study/cie-9618-u8-relational-database-model/) — Covers entities, attributes, relationships, keys, and entity-relationship (ER) diagram design.
- [Structured Query Language (SQL)](https://www.owlsprep.com/study/cie-9618-u8-structured-query-language/) — Teaches writing SQL for table creation, querying with filters/joins, and data manipulation.
- [Normalisation](https://www.owlsprep.com/study/cie-9618-u8-normalisation/) — Explains functional dependencies and how to normalise databases up to Third Normal Form (3NF).
- [Client-server and distributed databases](https://www.owlsprep.com/study/cie-9618-u8-client-server-and-distributed-databases/) — Compares different database architectures and the core properties of distributed database systems.
- [Transactions and concurrency control](https://www.owlsprep.com/study/cie-9618-u8-transactions-and-concurrency-control/) — Covers ACID properties and mechanisms to prevent conflicts from concurrent database access.

## Common pitfalls

- **Wrong:** Confusing primary keys and foreign keys when designing relational tables
  - Why it fails: This leads to incorrect joins and broken relationships between entities, costing marks in exam questions
  - Correct: Remember: primary keys uniquely identify a row in a table, while foreign keys reference a primary key in another table
- **Wrong:** Skipping all four ACID properties when answering exam questions on transactions
  - Why it fails: Most exam mark schemes require all four properties to award full marks
  - Correct: Memorise Atomicity, Consistency, Isolation, Durability and the definition of each property
- **Wrong:** Believing all databases must be normalised to 3NF in every case
  - Why it fails: Over-normalisation causes unnecessary performance overhead for read-heavy applications
  - Correct: Normalise to 3NF for most designs, but recognise when denormalisation is appropriate for performance

## Cheatsheet

| Key Concept | Description |
| --- | --- |
| Primary Key | Unique attribute that identifies each individual row in a relation |
| Foreign Key | Attribute that references the primary key of another relation to link entities |
| Third Normal Form (3NF) | No transitive functional dependencies; all non-key attributes depend only on the primary key |
| $SELECT ... FROM ... JOIN ... ON$ | Core SQL structure to query and combine data from multiple related tables |
| ACID Properties | Atomicity, Consistency, Isolation, Durability: required for reliable transaction processing |
| Client-Server Architecture | Centralised database stored on a server, accessed by multiple client devices over a network |

## What's next

Start with the first sub-topic to build your foundational understanding of database concepts, then work through the sequence to master design, implementation, and advanced management. Once you complete all sub-topics in this unit, you will move on to the next unit covering software engineering principles. Let's get started.

- [Database concepts (first sub-topic of this unit)](https://www.owlsprep.com/study/cie-9618-u8-database-concepts/)
- [Relational database model](https://www.owlsprep.com/study/cie-9618-u8-relational-database-model/)
- [Structured Query Language (SQL)](https://www.owlsprep.com/study/cie-9618-u8-structured-query-language/)

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