1.3.2 Flashcards
What is an entity?
An item which data is stored about
What is a relational database?
A database which stores each entity in its own table to identify the differences between them
What are attributes?
The characteristics of an entity
What is a flat file database?
The database consists of a single file with one entity
What is a primary key?
A unique identifier for each record in a table
What is a foreign key?
Links two tables together (the foreign key of one table is the primary key of another)
What is a secondary key?
This allows the database to be searched quickly
What is normalisation?
The process of producing the best possible layout for a database
What does normalisation sim to achieve?
- no redundancy
- consistent data in related tables
- records can be added/removed
- complex queries can be carried out
What is first normal form?
No attribute contains more than a single value
What is second normal form?
First normal form and has no partial dependencies (no attribute can depend on sort of a composite key)
What is third normal form?
Second normal form and has no non key dependencies (No field is dependent on another field which isn’t the primary key)
What is indexing?
A method of storing the position of each record ordered by a certain attribute
What is referential integrity?
Ensuring that data is not removed if it is needed elsewhere in a linked database
What is a transaction?
A single operation executed on data
What are the 4 components of ACID?
- atomicity
- consistency
- isolation
- durability
What does atomicity mean?
The transaction must be processed in its entirety it not at all
What does consistency mean?
It follows the rules of referential integrity
What does isolation mean?
Simultaneous transactions should give the same result as if they where executed one after another
What does durability mean?
Once a transaction is completed, it must remain so
What is record locking?
Preventing simultaneous access to records to prevent inconsistencies
What is redundancy?
Storing multiple copies of data in physically different locations to ensure data is not lost or damaged
