A Level Computer Science Paper 1: 1.3.2 Databases Part 2
Normalisation is the process of structuring a database to reduce redundancy and improve data integrity. It involves organizing data into tables that meet specific rules—starting with First Normal Form (1NF) and Second Normal Form (2NF)—to ensure each field depends fully on the primary key and that data is stored efficiently.
Normalisation
A process to come up with the best possible design for a database, organising tables so data is not duplicated in the same table or different tables.
Key Terms
Normalisation
A process to come up with the best possible design for a database, organising tables so data is not duplicated in the same table or different table...
First Normal Form
All field names must be unique
Values in fields should be from the same domain (only contain one piece/type of information)<...
Second Normal Form
It should already be in 1NF
Any partial dependencies have been removed (every field is dependent on the primary key)
Removing partial dependencies
Creating a second table for fields which can be inferred from another which isn’t the primary key. Create a linking table with each table’s primary...
Third Normal Form
The data is already in 2NF
2. Any transitive dependencies have been r...
Removing transitive dependencies
Create extra tables where the value of a field is determined by another which isn’t the primary key.
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| Term | Definition |
|---|---|
Normalisation | A process to come up with the best possible design for a database, organising tables so data is not duplicated in the same table or different tables. |
First Normal Form |
|
Second Normal Form |
|
Removing partial dependencies | Creating a second table for fields which can be inferred from another which isn’t the primary key. Create a linking table with each table’s primary key |
Third Normal Form |
2. Any transitive dependencies have been removed |
Removing transitive dependencies | Create extra tables where the value of a field is determined by another which isn’t the primary key. |
Normalisation advantages | Easier to maintain and manage |
EDI | Electronic Data Interchange - exchanges data between documents between computer systems, all documents must be in a standard format (can use EDI translation systems) |
Transaction | A single logical operation in a database, may consist of several operations, all of which must be processed. |
ACID | Atomicity, Consistency, Isolation, Durability - ensures the integrity of a database |
Atomicity | Requires that a transaction will be processed in its entirety or not at all |
| Ensures that no transaction can violate any of the defined validation rules |
Isolation | Ensures that each transaction will be isolated and dealt with in a way that does not affect others |
Durability | Once a transaction has been committed, it will remain so, even after a power cut. The data is held in a buffer |
Record locking | Prevents simultaneous access to objects in a database in order to prevent updates being lost or any inconsistencies. |
Deadlock | Where two users are trying to access the same record, serialism techniques are used to prevent it |
Timestamp Ordering | If the read timestamp of an object is different to when you opened it, another user must have accessed it so the transaction is cancelled |
Commitment Ordering | Orders transactions in terms of their dependencies on one another as well as the time of opening |
Redundancy | Stops systems going down with duplicate hardware in another location, now run on a backup |
| Changes are consistent across a database so removing a record removed all references to that record |
Indexing | A method to store the position of each record ordered by an attribute. The private key is automatically indexed but rarely queried |