Database 442 Quiz 1

entity

An entity is an object that exists and is distinguishable from other objects

entity set

An entity set is a set of entities of the same type that share the same properties.

relationship

A relationship is an association among several entities

relationship set

A relationship set is a mathematical relation among n ≥ 2 entities, each taken from entity sets

attribute

An attribute can also be property of a relationship set

domain

the set of permitted values for each attribute

For a binary relationship set the mapping cardinality must be one of the following types:

One to one

One to many

Many to one

Many to many

super key

A super key of an entity set is a set of one or more attributes whose values uniquely determine each entity

candidate key

A candidate key of an entity set is a minimal super key

primary key

a candidate key chosen as the principal means of

identifying tuples within a relation

weak entity set

An entity set that does not have a primary key is referred to as a weak entity set.

Attribute inheritance

a lower-level entity set inherits all the attributes and relationship participation of the higher-level entity set to which it is linked

relation schema

a tuple of related attributes

foreign key

A relation schema may have an attribute that corresponds to the primary key of another relation.

natural relationship

• two tables have a common attr/col. name

• same values in those columns

natural join removes…

removes duplicates

an operator creates…

a new table

database times

oltp

olap

oltp

online transaction

• normalizes the data, separate tables

• changes in real time

• used for fast transactions

olap

online analysis

• denormalizes data

• used to analyse information

• one table with data