1. CPSC-310 Database Systems
Professor Jianer Chen
Room 315C HRBB
Lecture #2
Source: modification of slides by Jeffrey Ullman of Stanford U.

2. Outline of Course Representing things by tables E-R model (Ch. 4)
Good table structures
Functional Dependencies (Ch. 3)
Basic operations on relations
Relational Algebra (Ch. 2)
Storage management
(Chs )
SQL languages in DDL/DML
(Ch. 6)
Query processing
(Chs )
More on SQL
(Chs. 7-9)
Transition processing
(Chs )

3. The Entity/Relationship Model
The E/R model is an intuitive (graphical) model used to sketch database designs, (where entity = object).

4. The Entity/Relationship Model
The E/R model is an intuitive (graphical) model used to sketch database designs, (where entity = object).
Properties of entities and how entities connect.
Not how to operate on entities.

5. The Entity/Relationship Model
The E/R model is an intuitive (graphical) model used to sketch database designs, (where entity = object).
Properties of entities and how entities connect.
Not how to operate on entities.
E/R designs are given by pictures (entity/relationship diagrams).

6. The Entity/Relationship Model
The E/R model is an intuitive (graphical) model used to sketch database designs, (where entity = object).
Properties of entities and how entities connect.
Not how to operate on entities.
E/R designs are given by pictures (entity/relationship diagrams).
It is in general straightforward to convert E/R designs to relational database designs.

7. Entity Sets
Entity = “thing” or object.

8. Entity Sets Entity = “thing” or object.
Entity set = collection of similar entities.
Similar to a class in object-oriented languages.

9. Entity Sets Entity = “thing” or object.
Entity set = collection of similar entities.
Similar to a class in object-oriented languages.
Attribute = property of (the entities of) an entity set.

10. Entity Sets Entity = “thing” or object.
Entity set = collection of similar entities.
Similar to a class in object-oriented languages.
Attribute = property of (the entities of) an entity set.
Attributes are of simple data types, e.g. integers or character strings.

11. E/R Diagrams
In an entity-relationship diagram:

12. E/R Diagrams In an entity-relationship diagram:
Entity set = rectangle.

13. E/R Diagrams In an entity-relationship diagram:
Entity set = rectangle.
Attribute = oval, with a line to the rectangle representing its entity set.

14. E/R Diagrams In an entity-relationship diagram: Example
Entity set = rectangle.
Attribute = oval, with a line to the rectangle representing its entity set.
Example
Entity set Beers has two attributes, name and manf (manufacturer)

15. E/R Diagrams In an entity-relationship diagram: Example
Entity set = rectangle.
Attribute = oval, with a line to the rectangle representing its entity set.
Example
Entity set Beers has two attributes, name and manf (manufacturer)
Each Beers entity has values for these two attributes. e.g. (Bud, Anheuser-Busch)

16. E/R Diagrams In an entity-relationship diagram: Example
Entity set = rectangle.
Attribute = oval, with a line to the rectangle representing its entity set.
Example
Entity set Beers has two attributes, name and manf (manufacturer)
Each Beers entity has values for these two attributes. e.g. (Bud, Anheuser-Busch)
Beers
name
manf

17. Relationships
A relationship connects some entity sets.

18. Relationships A relationship connects some entity sets.
It is given by a diamond, with lines to each of the entity sets involved.

19. Relationships A relationship connects some entity sets.
It is given by a diamond, with lines to each of the entity sets involved.
Bars
name
license
addr
name
manf
Beers
Drinkers
name
addr

20. Relationships A relationship connects some entity sets.
It is given by a diamond, with lines to each of the entity sets involved.
Bars sell some beers.
Bars
name
license
addr
name
manf
Beers
Drinkers
name
addr

21. Relationships A relationship connects some entity sets.
It is given by a diamond, with lines to each of the entity sets involved.
Bars sell some beers.
Bars
name
license
addr
name
manf
Sells
Beers
Drinkers
name
addr

22. Relationships A relationship connects some entity sets.
It is given by a diamond, with lines to each of the entity sets involved.
Bars sell some beers.
Bars
name
license
addr
name
manf
Sells
Beers
Likes
Drinkers like
some beers.
Drinkers
name
addr

23. Relationships A relationship connects some entity sets.
It is given by a diamond, with lines to each of the entity sets involved.
Bars sell some beers.
Bars
name
license
addr
name
manf
Sells
Beers
Frequents
Likes
Drinkers like
some beers.
Drinkers frequent
some bars.
Drinkers
name
addr

24. Relationship Set
The current “value” of an entity set is the set of entities that belong to it.
Example: the set of all bars in our database.
The “value” of a relationship is a set of lists of currently related entities, one from each of the related entity sets.
Bar Beer
Joe’s Bar Bud
Joe’s Bar Miller
Sue’s Bar Bud
Sue’s Bar Pete’s Ale
Sue’s Bar Bud Lite
For the relationship Sells, we might have a relationship set like:

25. Multiway Relationships
Sometimes, we need a relationship that connects more than two entity sets.

26. Multiway Relationships
Sometimes, we need a relationship that connects more than two entity sets.
Example.
Suppose that drinkers
will only drink certain beers at certain bars.

27. Multiway Relationships
Sometimes, we need a relationship that connects more than two entity sets.
Example.
Suppose that drinkers
will only drink certain beers at certain bars.
Our three binary relationships Likes, Sells, and Frequents do not allow us to make this distinction.

28. Multiway Relationships
Sometimes, we need a relationship that connects more than two entity sets.
Example.
Suppose that drinkers
will only drink certain beers at certain bars.
Our three binary relationships Likes, Sells, and Frequents do not allow us to make this distinction. But a 3-way relationship would.

29. Multiway Relationships
Sometimes, we need a relationship that connects more than two entity sets.
Example.
Suppose that drinkers
will only drink certain beers at certain bars.
Our three binary relationships Likes, Sells, and Frequents do not allow us to make this distinction. But a 3-way relationship would.
name
addr
name
Bars
Beers
Preferences
manf
license
Drinkers
name
addr

30. Multiway Relationships
Bar Drinker Beer
Joe’s Bar Ann Miller
Sue’s Bar Ann Bud
Sue’s Bar Ann Pete’s Ale
Joe’s Bar Bob Bud
Joe’s Bar Bob Miller
Joe’s Bar Cal Miller
Sue’s Bar Cal Bud Lite

31. Multiplicity of Relationships

32. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.

33. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a many-many relationship, an entity of either set can be connected to many entities of the other set.

34. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a many-many relationship, an entity of either set can be connected to many entities of the other set.
Example. a bar Sells many beers; a beer is sold by many bars.

35. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a many-many relationship, an entity of either set can be connected to many entities of the other set.
Example. a bar Sells many beers; a beer is sold by many bars.
Bars
Beers
A many-many
relationship
Sells

36. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a many-one relationship, an entity in one A of the entity sets is connected to at most one entity of the other entity set B, but an entity of B can be connected any number of entities of A.

37. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a many-one relationship, an entity in one A of the entity sets is connected to at most one entity of the other entity set B, but an entity of B can be connected any number of entities of A. Example. Favorite, from Drinkers to Beers is many-one.

38. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a many-one relationship, an entity in one A of the entity sets is connected to at most one entity of the other entity set B, but an entity of B can be connected any number of entities of A. Example. Favorite, from Drinkers to Beers is many-one.
Drinkers
Beers
A many-one
relationship
Favorite

39. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a one-one relationship, each entity of either entity set is related to at most one entity of the other set.

40. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a one-one relationship, each entity of either entity set is related to at most one entity of the other set Example. Relationship Best-seller between entity sets Manfs (manufacturer) and Beers.

41. Multiplicity of Relationships
We consider binary relationships, i.e., relationship between two entity sets.
In a one-one relationship, each entity of either entity set is related to at most one entity of the other set Example. Relationship Best-seller between entity sets Manfs (manufacturer) and Beers.
Manfs
Beers
A one-one
relationship
Best-seller

42. Representing “Multiplicity”

43. Representing “Multiplicity”
Show a many-one relationship by an arrow entering the “one” side.

44. Representing “Multiplicity”
Show a many-one relationship by an arrow entering the “one” side.
Show a one-one relationship by arrows entering both entity sets.

45. Representing “Multiplicity”
Show a many-one relationship by an arrow entering the “one” side.
Show a one-one relationship by arrows entering both entity sets.
Rounded arrow = “exactly one,” i.e., each entity of the first set is related to exactly one entity of the target set.

46. Representing “Multiplicity”
Show a many-one relationship by an arrow entering the “one” side.
Show a one-one relationship by arrows entering both entity sets.
Rounded arrow = “exactly one,” i.e., each entity of the first set is related to exactly one entity of the target set.
Drinkers
Beers
Likes
Favorite

47. Example
Consider Best-seller between Manfs and Beers.

48. Example Consider Best-seller between Manfs and Beers.
Some beers are not the best-seller of any manufacturer, so a rounded arrow to Manfs would be inappropriate.

49. Example Consider Best-seller between Manfs and Beers.
Some beers are not the best-seller of any manufacturer, so a rounded arrow to Manfs would be inappropriate.
But a beer manufacturer has to have a best-seller.

50. Example Consider Best-seller between Manfs and Beers.
Some beers are not the best-seller of any manufacturer, so a rounded arrow to Manfs would be inappropriate.
But a beer manufacturer has to have a best-seller.
Manfs
Beers
Best-
seller

51. Attributes on Relationships
Sometimes it is useful to attach an attribute to a relationship.

52. Attributes on Relationships
Sometimes it is useful to attach an attribute to a relationship.
Think of this attribute as a property of tuples in the relationship set.

53. Attributes on Relationships
Sometimes it is useful to attach an attribute to a relationship.
Think of this attribute as a property of tuples in the relationship set.
Example. Price is a function of both the bar and the beer, not of one alone.
Bars
Beers
Sells
price

54. Attributes on Relationships
Sometimes it is useful to attach an attribute to a relationship.
Think of this attribute as a property of tuples in the relationship set.
Example. Price is a function of both the bar and the beer, not of one alone.
Equivalently, you can create an entity set representing values of the attribute, and make that entity set participate in the relationship.
Bars
Beers
Sells
price

55. Attributes on Relationships
Sometimes it is useful to attach an attribute to a relationship.
Think of this attribute as a property of tuples in the relationship set.
Example. Price is a function of both the bar and the beer, not of one alone.
Equivalently, you can create an entity set representing values of the attribute, and make that entity set participate in the relationship.
Bars
Sells
Beers
price
Bars
Beers
Sells
price
Prices

56. Attributes on Relationships
Sometimes it is useful to attach an attribute to a relationship.
Think of this attribute as a property of tuples in the relationship set.
Example. Price is a function of both the bar and the beer, not of one alone.
Equivalently, you can create an entity set representing values of the attribute, and make that entity set participate in the relationship.
Bars
Sells
Beers
price
Bars
Beers
Sells
price
Prices
Note convention: arrow
from multiway relationship
means “all other entity
sets together determine a
unique one of these.”