Computer Science
What is an 'Attribute'
Attribute - Describes the details/characteristics of an object or person
Define a 'Database'
An organised collection of data
Give 3 benefits of using electronic databases
- Easier to retrieve, add, delete and modify data
- Easier to backup
- Can be accessed by multiple people at the same time
What is a 'Flat File' database
A simple database structure which is uses one table to hold all data/info
What is a 'primary key'
A field that uniquely identifies each record
What is a 'foreign key'
An attribute that joins two tables together
Define 'Querying'
Finding data within a database
What is a DBMS and what does it do
DBMS(Database Management System) provides a layer of abstraction for the user and programmer
Give 2 ways a DBMS hide the underlying structure of data
- Prevents duplicate primary keys being made
- Enforces validation rules
Give 3 manual methods of exchanging data between databases
- Memory stick
- Optical media
- Emaiil
- Paper based
Give a disadvantage of capturing data as a paper based form
- Humans can make errors
- It is slower
Give 2 automated ways of capturing data and state their advantages
OCR (Optical Character Recognition)
OMR( Optical Mark Recognition)
Captures data much quicker
Reduces human error
Manual methods of capturing data is slow, give another form of capturing data
EDI (Electronic Data Interchange) - Where data is automatically read & transferred from one computer to another
What conditions must be met for a database to be in first normal form
- All field names must be unique
- Values in the same field must have the same domain(have the same value)
- Values in fields must be atomic(one value per field)
- No records can be identical
- Each table needs a primary key
What conditions must be met for a database to be in second normal form
- The data must be in 1NF
- There must be no partial dependencies (where one/more fields depend on part of the primary key)
What conditions must be met for a database to be in third normal form
- Must be in 2NF
- Transitive dependencies must be removed (Where a value depends on another field that isn't the primary key)
Give 3 formats of storing and transferring data
- JSON
- XML
- CSV
Name 2 query languages and what they allow you to do
SQL(Structured Query Language) | QBE(Query By Example)
- Allows you to Specify tables
- Allows you to Specify criteria
- Allows you to Specify fields
- Use boolean expressions
Give benefits of organising data into a database
Makes in easy to:
- Add data
- Modify data
- Delete data
- Search data
Define 'Transaction Processing'
Any information processing that's divided into individual, indivisible operations called transactions
In each transaction, what must you ensure?
The transaction must succeed or fail, it should never be partially complete
What must each transaction do to ensure data integrity (complete data)
The transactions processing must follow a set of rules known as ACID. ATOMICITY CONSISTENCY ISOLATION DURABILITY.
Define 'Atomicity' (IN ACID)
Where a change to a database must be completely done or not done at all. Half changes must not be saved
Define 'Consistency' (IN ACID)
Any change in the database must retain the overal state of the database
Define 'Isolation' (IN ACID)
Where a transaction mustn't be interrupted by another transaction. It must occur in isolation so that other processes/other users can't access the data concerned.
How is Isolation implemented
The DBMS enforces Isolation via record locking. This locks any records that are affected via transactions. Putting them in a read only state.
Define 'Record Locking'
A technique that's used to prevent multiple users accessing the same object/record in a database at the same time. This prevents data inconsistencies
Define 'Durability' (IN ACID)
Where once a change is made to a database, it mustn't get lost due to system/power failure
How is durability implemented
The DBMS writes the effects of the transactions immediately back to the secondary storage rather than holding any changes in any form of volatile memory
What does 'Referental Integrity' do
Ensures consistency between related tables in a relational database