data management foundations

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12 Terms

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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.

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cardinality

refers to maxima and minima of relationships and attributes


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Relationship maximum

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


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 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.


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Normalization

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

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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

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first normal form table

every non-key column depends on the primary key.

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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.

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