N-ary relations and their applications. (Rosen 8.2)

Сентябрь 14, 2022

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N-ary relations and their applications. (Rosen 8.2)

Содержание

2. n-ary relations We can have relation between more than just 2 sets A binary relation involves
3. n-ary relations n-ary Relations
4. n-ary relations n-ary Relations Note: N is the set of natural numbers {0,1,2,3,…} An example Note:
5. n-ary relations n-ary Relations Note: N is the set of natural numbers {0,1,2,3,…} Z is the
6. Relational databases Database is made up of records. Typical operations on a database are find records
9. Relational databases The relational data model Database made up of records, they are n-tuples, made up
10. Relational databases The relational data model Example from the book Attributes: name, metric No, Dept and
11. Relational databases The relational data model primary key: An attribute/domain/column is a primary key when the
12. Relational databases The relational data model The current collection of n-tuples (records) in the relation (table)
13. Relational databases The relational data model A composite key is a combination of attributes That uniquely
14. Relational databases Operations on n-ary relations Selection
15. Relational databases Operations on n-ary relations Selection
16. Relational databases Operations on n-ary relations Projection It strips out specific columns
17. Relational databases Operations on n-ary relations Projection
18. Relational databases Operations on n-ary relations Join Joins two tables/relations together, matching up on specific attributes
19. Relational databases Operations on n-ary relations Join
21. Скачать презентацию

Слайд 2

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!

Слайд 3

n-ary relations
n-ary Relations

Слайд 4

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

Слайд 5

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

Слайд 6

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

are
find records that satisfy a given criteria
delete records
add records
update records

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

Databases may be represented
using the relational model

Слайд 7

Слайд 8

Слайд 9

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

Слайд 10

Relational databases
The relational data model
Example from the book
Attributes: name, metric No,

Dept and GPA

Слайд 11

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

Слайд 12

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

Слайд 13

Relational databases
The relational data model
A composite key is a combination of

attributes
That uniquely define tuples

Слайд 14

Relational databases
Operations on n-ary relations
Selection

Слайд 15

Relational databases
Operations on n-ary relations
Selection

Слайд 16

Relational databases
Operations on n-ary relations
Projection
It strips out specific columns

Слайд 17

Relational databases
Operations on n-ary relations
Projection

Слайд 18

Relational databases
Operations on n-ary relations
Join
Joins two tables/relations together, matching up on

specific attributes

Слайд 19

N-ary relations and their applications. (Rosen 8.2)

Содержание

n-ary relationsWe can have relation between more than just 2 setsA

n-ary relationsn-ary Relations

n-ary relationsn-ary RelationsNote: N is the set of natural numbers {0,1,2,3,…}An

n-ary relationsn-ary RelationsNote: N is the set of natural numbers {0,1,2,3,…}

Relational databasesDatabase is made up of records.Typical operations on a database

Relational databasesThe relational data modelDatabase made up of records, they are

Relational databasesThe relational data modelExample from the bookAttributes: name, metric No,

Relational databasesThe relational data modelprimary key:An attribute/domain/column is a primary key

Relational databasesThe relational data modelThe current collection of n-tuples (records) in

Relational databasesThe relational data modelA composite key is a combination of

Relational databasesOperations on n-ary relationsSelection

Relational databasesOperations on n-ary relationsSelection

Relational databasesOperations on n-ary relationsProjectionIt strips out specific columns

Relational databasesOperations on n-ary relationsProjection

Relational databasesOperations on n-ary relationsJoinJoins two tables/relations together, matching up on

Relational databasesOperations on n-ary relationsJoin

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