exchanging data (databases) Flashcards
What are relational databases?
An entity is an item of Interest of which info is stored. Relational databases recognise differences between entities by creating tables for each entity.
What is a flat file database?
A database which consists of a single file. Usually based on a single key and its attributes.
What is a primary key?
Unique identifier for each record in a table. Like an ID.
What is a foreign key?
Attribute that links 2 tables together. Exists as primary key in one table and foreign key in another.
What is a secondary key?
Allows for a database to be searched quickly. Like a surname.
What are the 3 entity relationship models?
One to one
One to many
Many to many
Explain first normal form?
There must be no attribute containing more than a single value.
Explain second normal form?
A database with no partial dependencies and is in first normal form. Meaning no attributes can depend on part of a composite key.
Explain third normal form?
Must be in second normal form and contain no non key dependencies. This means an attribute depends on the value of the primary key.
Explain referential integrity?
The process of ensuring consistency.
Explain ACID
Atomicity - A transaction must be processed fully or not at all
Consistency - A transaction must maintain referential integrity rules between linked tables.
Isolation - Transactions at the same time must lead to the same result as if they were done at the same time.
Durability - Once a transition is executed it will remain so.
Explain record locking?
This prevents simultaneous access to records within a database. Prevents inconsistencies or loss of updates.
Explain redundancy?
Companies have one or more copies of the same data in physically different locations. If one is damaged it can be recovered.
