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N-ary relations and their applications. (Rosen 8.2) презентация
Содержание
- 1. N-ary relations and their applications. (Rosen 8.2)
- 2. n-ary relations We can have relation between
- 3. n-ary relations n-ary Relations
- 4. n-ary relations n-ary Relations Note: N is
- 5. n-ary relations n-ary Relations Note: N is
- 6. Relational databases Database is made up of
- 9. Relational databases The relational data model Database
- 10. Relational databases The relational data model Example
- 11. Relational databases The relational data model primary
- 12. Relational databases The relational data model The
- 13. Relational databases The relational data model A
- 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
- 19. Relational databases Operations on n-ary relations Join
- 20. Explain the previous slide Explain how what
Слайд 2n-ary relations
We can have relation between more than just 2 sets
A
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 4n-ary relations
n-ary Relations
Note: N is the set of natural numbers {0,1,2,3,…}
An
Note: R could be considered as an extensional representation of the The relation has degree 3 The domains of the relation are the set of natural numbers
ternary relation a
Слайд 5n-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 The relation has degree 4
ternary relation a
Слайд 6Relational databases
Database is made up of records.
Typical operations on a database
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 9Relational databases
The relational data model
Database made up of records, they are
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 10Relational databases
The relational data model
Example from the book
Attributes: name, metric No,
Слайд 11Relational databases
The relational data model
primary key:
An attribute/domain/column is a primary key
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 12Relational databases
The relational data model
The current collection of n-tuples (records) in
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 13Relational databases
The relational data model
A composite key is a combination of
That uniquely define tuples
Слайд 18Relational databases
Operations on n-ary relations
Join
Joins two tables/relations together, matching up on
