1. From data needs to ER Model to relational DB Schema
Db Design Process
From data needs to ER Model to relational DB Schema

2. NBA.com: the needs

3. What are the Entity sets?
Name ID
Type ?
Location ?
Location
All “things” that listed in the banners?
Entity (set) vs. Attribute:
Should Location be an entity or an attribute?
Team

4. 2 relationships btw 2 entity sets: Is it possible?
In every game, there are two teams engaged:
One as the home team
Another as away team
Which one gives the correct answer?
Game
Game
hasHm
hasAw
home
away OR
HomeTeam
AwayTeam
Team

5. Recursive relationship: what is it?
Isn’t it true that each team just has one coach?
What about specialty coaches and all the training staff?
How to keep track them all and model the reporting structure?
Team
has
reportsTo
chief
Coach
asst

6. Relationship set or Entity Set: do it matter?
Can I model the Game as a recursive relationship btw 2 (team) instances in the same Team entity sets?
Would the outcome be any different?
Game
home
PlaysAs
away
PlaysAs OR
EngagedIn
Team
Game
home
Team
away

7. The big picture: is it complete?

8. Cardinality constraints: why is it important?
Three options
1:1
1:M/M:1
M:M (or M:N)
# of tables needed
1 (or two, with other considerations)
2: with FK added to the many side
3: with a junction table for m:m mapping info  which is as important as value in the attributes!

9. Convert into relational model
Tables and columns:
Each entity set becomes a table
A many-to-many relationship set becomes a table
Each (atomic) attribute becomes a column
Keys:
“Composite” key in the junction tables: PK from both related entity sets
Surrogate key: independent from changes in business domain

10. Foreign keys
FK specifies a constraint btw a referencing table and a referenced table
It’s not a key in the referencing table (although may be part of the key)
It’s a key in the referenced table (often the PK, but can be any candidate keys)
It has as many attr’s (or columns) as its referenced key
It’s added to the table on the many-side during the conversion
Referential integrity can be enforced by requiring FK to take values existing in its referenced key

11. More Complex situations: N-ary
What is N-ary (relationship)?
All relationships that we discussed so far are binary? Can a R involve more E’s?
Think about the PlayerStats entity set: it actually relates
Player,
Game in which a Player plays, and
An entity in the StatsCategory entity set
Common practice is to convert a N-ary R into N binary ones

12. More Complex situations: attributes
Composite attributes
Name
Address
Multi-valued attributes
Player position: multiple positions at the same time, or during different periods
Player stats or performance history

13. More Complex situations: weak entity
Section of Course
Section cannot exist without a Course
Section has only got a partial key: (Section_No, Year, Semester)
It needs to borrow PK from Course: (Course_No) to form a unique of its own: (Course_No , Section_No, Year, Semester)
Course
has
Section