Databases

Entity

An object of Interest to an organisation which data is recorded about

Atribute

A characteristic of an entity

Primary Key

An identifier for an entity which identifies each record within it uniquley

Relationship

An association between two entities

What is needed for first normal form?

• Each column is atomic

What is needed for 2NF

• There must be only one primary key

• There must be no partial dependencies

What is needed for 3NF

• There must be no transitive dependencies

What is a partial dependency?

When attributes depend on only part of a composite key

What is a transitive dependency

When a attribute does not depend on the primary key

What is a relational database?

A structured system for managing and retrieving data

What is concurrent access?

When two users try to access the same field in a database at once

Define record locking

When a user tries to edit a record, the record becomes locked so other users can’t modify it. Once they are finished, the record becomes unlocked

What is serialisation?

When multiple users try to edit the record, their commands get placed in a queue. Once the first user is finished, the next command executes and so on.

What is timestamp ordering?

When concurrent access occurs, each command is given a time stamp. The commands are operated on the field in order of the timestamps

What is commitment ordering?

When concurrent access occurs, an algorithm chooses which order to execute them in…