data management foundations

Entity-relationship-attribute

Entity-relationship-attribute

• An entity is a person, place, product, concept, or activity.

• A relationship is a statement about two entities.

• An attribute is a descript­ive property of an entity.

cardinality

refers to maxima and minima of relationships and attributes

Relationship maximum

is the greatest number of instances of one entity that can relate to a single instance of another entity.

 Maxima

A relationship has two maxima, one for each of the related entities.

 Maxima are usually specified as one or many. 

A related entity is singular when the maximum is one and plural when the maximum is many.

Normalization

eliminates redundancy by decomposing a table into two or more tables in higher normal form

Dependency

 (causes redundancy when B is not unique)

 Column A depends on column B means each B value is related to at most one A value :  B → A

Since a passenger number (A) always identifies the same passenger name (B), PassengerName depends on PassengerNumber

first normal form table

every non-key column depends on the primary key.

second normal form

when all non-key columns depend on the whole primary key. In other words, a non-key column cannot depend on part of a composite primary key.