1. Conceptual Database Design

2. Building an Application with a DBMS
Requirements modeling (conceptual, pictures)
Decide what entities should be part of the application and how they should be linked.
Schema design and implementation
Decide on a set of tables, attributes.
Define the tables in the database system.
Populate database (insert tuples).
Write application programs using the DBMS
way easier now that the data management is taken care of.

3. Database Design Why do we need it? Consider issues such as:
Agree on structure of the database before deciding on a particular implementation.
Consider issues such as:
What entities to model
How entities are related
What constraints exist in the domain
How to achieve good designs

4. Database Design Formalisms
1. Object Definition Language (ODL):
Closer in spirit to object-oriented models
I don’t teach it anymore.
2. Entity/Relationship model (E/R):
More relational in nature.
Both can be translated (semi-automatically) to relational schemas
ODL to OO-schema: direct transformation (C++ or Smalltalk based system).

5. 2. Entity / Relationship Diagrams
Entities
Attributes
Relationships between entities
Product
address
buys

6. Keys in E/R Diagrams Every entity set must have a key name category
price
Product

7. name
category
name
price
makes
Company
Product
stockprice
buys
employs
Person
name
ssn
address

8. What is a Relation ? A mathematical definition:
if A, B are sets, then a relation R is a subset of A x B
A={1,2,3}, B={a,b,c,d},
R = {(1,a), (1,c), (3,b)}
- makes is a subset of Product x Company: 1 2 3 a b c d A= B=
makes
Company
Product

9. Multiplicity of E/R Relations
one-one:
many-one
many-many 1 2 3 a b c d 1 2 3 a b c d 1 2 3 a b c d

10. name
category
name
price
makes
Company
Product
stockprice
What does this say ?
buys
employs
Person
name
ssn
address

11. Multi-way Relationships
How do we model a purchase relationship between buyers,
products and stores?
Purchase
Product
Person
Store
Can still model as a mathematical set (how ?)

12. Arrows in Multiway Relationships
Q: what does the arrow mean ?
A: if I know the store, person, invoice, I know the movie too
Rental
VideoStore
Person
Movie
Invoice

13. Arrows in Multiway Relationships
Q: what do these arrow mean ?
A: store, person, invoice determines movie and store, invoice, movie determines person
Invoice
VideoStore
Rental
Movie
Person

14. Arrows in Multiway Relationships
Q: how do I say: “invoice determines store” ?
A: no good way; best approximation:
Q: Why is this incomplete ?
Rental
VideoStore
Person
Movie
Invoice

15. Roles in Relationships
What if we need an entity set twice in one relationship?
Product
Purchase
Store
buyer
salesperson
Person

16. Attributes on Relationships
date
Product
Purchase
Store
Person

17. Converting Multi-way Relationships to Binary
ProductOf
date
Product
Purchase
StoreOf
Store
BuyerOf
Person

18. From E/R Diagrams to Relational Schema
Entity set  relation
Relationship  relation

19. Entity Set to Relation name category price Product
Product(name, category, price)
name category price
gizmo gadgets $19.99

20. Relationships to Relations
price
name
category
Start Year
name
makes
Company
Product
Stock price
Makes(product-name, product-category, company-name, year) Product-name Product-Category Company-name Starting-year
gizmo gadgets gizmoWorks
(watch out for attribute name conflicts)

21. Relationships to Relations
price
name
category
Start Year
name
makes
Company
Product
Stock price
No need for Makes. Modify Product:
name category price StartYear companyName
gizmo gadgets gizmoWorks

22. Multi-way Relationships to Relations
address
name
Product
Purchase
price
Store
name
Person
Purchase( , , )
ssn
name

23. 3. Design Principles What’s wrong? Purchase Product Person President
Country
Person
Moral: be faithful!

24. Design Principles: What’s Wrong?
date
Product
Purchase
Store
Moral: pick the right
kind of entities.
personAddr
personName

25. Design Principles: What’s Wrong?
date
Dates
Product
Purchase
Store
Moral: don’t
complicate life more
than it already is.
Person