diagram is widely used in database design
Represent conceptual level
of a database systemDescribe things and their relationships in high level
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Презентация на тему ER – entity relationship diagram major components of ER diagram. (Chapter 6)
Содержание
- 2. *Yan Huang - ERER1976 proposed by Peter
- 3. *Yan Huang - ERBasic ConceptsEntity set –
- 4. *Yan Huang - ERAn Example
- 5. *Yan Huang - ERRelationshipA relationship may be
- 6. *Yan Huang - ERRelationshipA relationship set is
- 7. *Yan Huang - ERRelationship Example
- 8. *Yan Huang - ERAttribute of A Relationship Set
- 9. *Yan Huang - ERRelationshipThe degree of a
- 10. *Yan Huang - EROne-One and One-Many
- 11. *Yan Huang - ERMany-one and many-many
- 12. *Yan Huang - ER1- many
- 13. *Yan Huang - ERMany - 1
- 14. *Yan Huang - ERMany - many
- 15. *Yan Huang -CSCE4350 - ERAlternative Cardinality Specification
- 16. *Yan Huang - ERNote on Mapping CardinalityBoth
- 17. *Yan Huang - ERTotal ParticipationWhen we require
- 18. *Yan Huang - ERSelf RelationshipSometimes entities in
- 19. *Yan Huang - ERMore examples on self-relationshipPeople
- 20. *Yan Huang 350 - ERAttributesBoth entity sets
- 21. *Yan Huang - ERAnother Example
- 22. *Yan Huang - ERKeysA super key of
- 23. *Yan Huang - ERKey ExamplesSuggest super keys for the following entity?What are the candidate keys?Primary key?authornamebirthdaydeathdescription
- 24. *Yan Huang - - ERTernary Relationship
- 25. *Yan Huang - ERCan We Decompose a
- 26. *Yan Huang - ERConverting Ternary to binaryIn
- 27. *Yan Huang - ERConverting Ternary to binary
- 28. *Yan Huang - ERDesign an ER DiagramDesign
- 29. *Yan Huang - ERWeak Entity SetSome entity
- 30. *Yan Huang - ERWeak Entity Set NotationsDouble
- 31. *Yan Huang - ERSpecializationA lower-level entity set
- 32. *Yan Huang - ER
- 33. *Yan Huang - ERSpecificationDisjointCompleteness constraint (use double
- 34. *Yan Huang - ERDesign ConsiderationsUse of entity
- 35. *Yan Huang - ERNotations
- 36. *Yan Huang - ERNotations
- 37. *Yan Huang - ERER Practice AgainDesign an
- 38. *Yan Huang CE4350 - ERBest Practice Guide
- 39. *Yan Huang - ERER for Banking EnterpriseDescription handhout
- 40. *Yan Huang - ERRead ER DiagramsFollowing are some ER diagrams grabbed from the webRead to understand/criticize
- 41. *Yan Huang - ER?????????
- 42. *Yan Huang -CSCE4350 - ER?????
- 43. *Yan Huang -CSCE4350 - ER?
- 44. Скачать презентацию
- 45. Похожие презентации
*Yan Huang - ERER1976 proposed by Peter ChenER diagram is widely used in database designRepresent conceptual level of a database systemDescribe things and their relationships in high level
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Yan Huang - ER
ER
1976 proposed by Peter Chen
ER
diagram is widely used in database design
of a database systemDescribe things and their relationships in high level
Слайд 3
*
Yan Huang - ER
Basic Concepts
Entity set – an
abstraction of similar things, e.g. cars, students
An entity
set contains many entitiesAttributes: common properties of the entities in a entity sets
Relationship – specify the relations among entities from two or more entity sets
Слайд 5
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Yan Huang - ER
Relationship
A relationship may be thought
as a set as well
For binary relationship, it enumerates
the pairs of entities that relate to each otherFor example, entity set M = {Mike, Jack, Tom} entity set F = {Mary, Kate}. The relationship set married between M and F may be {
Слайд 6
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Yan Huang - ER
Relationship
A relationship set is a
mathematical relation among n ≥ 2 entities, each taken
from entity sets{(e1, e2, … en) | e1 ∈ E1, e2 ∈ E2, …, en ∈ En} where (e1, e2, …, en) is a relationship
Example:
(Hayes, A-102) ∈ depositor
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Yan Huang - ER
Relationship
The degree of a relationship
= the number of entity sets that participate in
the relationshipMostly binary relationships
Sometimes more
Mapping cardinality of a relationship
1 –1
1 – many
many – 1
Many-many
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Yan Huang - ER
Note on Mapping Cardinality
Both many
and 1 include 0
Meaning some entity may not participate
in the relationship
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Yan Huang - ER
Total Participation
When we require all
entities to participate in the relationship (total participation), we
use double lines to specifyEvery loan has to have at least one customer
Слайд 18
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Yan Huang - ER
Self Relationship
Sometimes entities in a
entity set may relate to other entities in the
same set. Thus self relationshipHere employees mange some other employees
The labels “manger” and “worker” are called roles the self relationship
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Yan Huang - ER
More examples on self-relationship
People to
people
Parent – children
Manager – employee
Husband – wife
Word to word
Root
– synonym
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Yan Huang 350 - ER
Attributes
Both entity sets and
relationships can have attributes
Attributes may be
Composite
Multi-valued (double ellipse)
Derive
(dashed ellipse)
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Yan Huang - ER
Keys
A super key of an
entity set is a set of one or more
attributes whose values uniquely determine each entity.A candidate key of an entity set is a minimal super key
Although several candidate keys may exist, one of the candidate keys is selected to be the primary key.
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Yan Huang - ER
Key Examples
Suggest super keys for
the following entity?
What are the candidate keys?
Primary key?
author
name
birthday
death
description
Слайд 25
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Yan Huang - ER
Can We Decompose a Ternary
Relationship?
Some relationships that appear to be non-binary may be
better represented using binary relationshipsE.g. A ternary relationship parents, relating a child to his/her father and mother, is best replaced by two binary relationships, father and mother
Using two binary relationships allows partial information (e.g. only mother being know)
But there are some relationships that are naturally non-binary
E.g. works-on, why?
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Yan Huang - ER
Converting Ternary to binary
In general,
any non-binary relationship can be represented using binary relationships
by creating an artificial entity set.Replace R between entity sets A, B and C by an entity set E, and three relationship sets:
1. RA, relating E and A 2.RB, relating E and B
3. RC, relating E and C
Create a special identifying attribute for E
Add any attributes of R to E
For each relationship (ai , bi , ci) in R, create
1. a new entity ei in the entity set E 2. add (ei , ai ) to RA
3. add (ei , bi ) to RB 4. add (ei , ci ) to RC
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Yan Huang - ER
Design an ER Diagram
Design a
database for an on-line reservation system for microscopes in
material science labThere are two types of users: microscope administrators and microscope end users
Each microscope is located in a specific lab
Each request is assigned to an administrator who can authorize or deny the request
Using of some microscope requires the presence of an administrator
Time is divided into 1 hour slots. Each reservation can only take one or more time slots
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Yan Huang - ER
Weak Entity Set
Some entity sets
in real world naturally depend on some other entity
setThey can be uniquely identified only if combined with another entity set
Example:
section1, section2, … become unique only if you put them into a context, e.g. csce4350
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Yan Huang - ER
Weak Entity Set Notations
Double rectangles
for weak entity set
Double diamond for weak entity relationship
Dashed
underscore for discriminator
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Yan Huang - ER
Specialization
A lower-level entity set inherits
all the attributes and relationship participation of the higher-level
entity set to which it is linked.A lower-level entity set may have additional attributes and participate in additional relationships
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Yan Huang - ER
Specification
Disjoint
Completeness constraint (use double lines)
total
: an entity must belong to one of the
lower-level entity setspartial: an entity need not belong to one of the lower-level entity sets
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Yan Huang - ER
Design Considerations
Use of entity sets
vs. attributes
Whether we want to keep additional information
Use of
entity sets vs. relationship setsActions among entities are usually represented by relationships
Binary versus n-ary relationship sets
N-nary relationships are usually more natural for actions among entity sets
Weak entity set vs. strong entity set
Generalization
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Yan Huang - ER
ER Practice Again
Design an ER
diagram for an online music store. The database will
contain at least the following concepts: songs, artists, bands, albums, and genres.State your design assumptions you make to support design decisions. Be sure your assumptions are reasonable.
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Yan Huang CE4350 - ER
Best Practice Guide for
ER Design
Use of entity sets vs. attributes
Use of entity
sets vs. relationship setsBinary versus n-ary relationship sets
Weak entity set vs. strong entity set
Choose the natural one
Generalization
If specialized entities need to keep additional information and participate in additional relationships
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Yan Huang - ER
Read ER Diagrams
Following are some
