# Презентация на тему N-ary relations and their applications. (Rosen 8.2)

Презентация на тему Презентация на тему N-ary relations and their applications. (Rosen 8.2), предмет презентации: Математика. Этот материал содержит 20 слайдов. Красочные слайды и илюстрации помогут Вам заинтересовать свою аудиторию. Для просмотра воспользуйтесь проигрывателем, если материал оказался полезным для Вас - поделитесь им с друзьями с помощью социальных кнопок и добавьте наш сайт презентаций ThePresentation.ru в закладки!

## Слайды и текст этой презентации

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n-ary Relations and Their Applications

Rosen 8.2

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n-ary relations

We can have relation between more than just 2 sets

A binary relation involves 2 sets and can be described by a set of pairs
A ternary relation involves 3 sets and can be described by a set of triples

An n-ary relation involves n sets and can be described by a set of n-tuples

Relations are used to represent computer databases

Also used to represent constraints!

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n-ary relations

n-ary Relations

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n-ary relations

n-ary Relations

Note: N is the set of natural numbers {0,1,2,3,…}

An example

Note: R could be considered as an extensional representation of the
ternary relation a

The relation has degree 3

The domains of the relation are the set of natural numbers

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n-ary relations

n-ary Relations

Note: N is the set of natural numbers {0,1,2,3,…}
Z is the set of integers {…,-2,-1,0,1,2,…}

An example

Note: R could be considered as an extensional representation of the
ternary relation a

The relation has degree 4

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Relational databases

Database is made up of records.
Typical operations on a database are

find records that satisfy a given criteria
delete records
update records

Some everyday databases
student records
health records
tax information
telephone directories
banking records

Databases may be represented
using the relational model

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Relational databases

The relational data model

Database made up of records, they are n-tuples, made up of fields

Student record might look as follows

(name,metricNo,faculty,gpa)

(Jones,200401986,Arts,4.9)
(Lee,200408972,Science,3.6)
(Kuhns,200501728,Humanities,5.0)
(Moore,200308327,Science,5.5)

relations (in relDB) also called tables

gpa is an attribute

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Relational databases

The relational data model

Example from the book

Attributes: name, metric No, Dept and GPA

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Relational databases

The relational data model

primary key:
An attribute/domain/column is a primary key when
the value of this attribute uniquely defines tuples
i.e. no two tuples have the same value for that attribute

Name cannot be a primary key, neither can Dept or GPS
metricNo is a primary key

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Relational databases

The relational data model

The current collection of n-tuples (records) in the relation (table)
is called the extension of the relation

The permanent aspects of the relation (table) such as the attribute names
is called the intention of the relation

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Relational databases

The relational data model

A composite key is a combination of attributes
That uniquely define tuples

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Relational databases

Operations on n-ary relations

Selection

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Relational databases

Operations on n-ary relations

Selection

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Relational databases

Operations on n-ary relations

Projection

It strips out specific columns

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Relational databases

Operations on n-ary relations

Projection

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Relational databases

Operations on n-ary relations

Join

Joins two tables/relations together, matching up on specific attributes

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Relational databases

Operations on n-ary relations

Join

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Explain the previous slide

Explain how what we do differs from what will
be presented in IM2

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