Databases Flashcards
(20 cards)
What’s a database management system?
A database management system is a software system that enables the management of a database. E.g access, SQL, ORACLE
Define the word database
A database is a structured collection of data
What’s a data model
A method of describing the data, it’s stucture.
What’s an entity
An entity is an object/person/event about which data is recorded
What’s a relationship?
A relationship is an association or link between two entities
What are names for a row?
A record or a tuple
What are other names for a column
Field and attribute
What is entity occurrence
The details of one instance of the entity
What’s a primary key
An unique attribute which uniquely identify a tuple
Relational database is?
A collection of tables
What’s composite key
A combination of attributes that uniquely identify a tuple
What’s a foreign key?
An attribute in one table that is a primary key in another table
What is meant by normalised entities
A set of entities that contain no useless/redundant data
What’s normalisation
A technique used to produce a set of normalised entities
What’s 1NF
Table have primary key and there’s no repeating groups of attributes (atomic values)
What’s 2NF
Must be 1NF and contain no partial key dependencies - where the values of the attributes are all independent on the primary key
What’s 3NF
Table is in third normal from if it is in 2NF and where no attributes are predictable because of any other attributes
What does SQL stands for?
Structured query language
Why is 3NF important?
It improves consistency
No unnecessarily repeated data
Eliminate update/insertion/deletion anomalies
What does 3NF means
Every attribute is dependent on the key, the whole key and nothing but the key.
