1. EECS 647: Introduction to Database Systems
Instructor: Luke Huan
Spring 2007

2. Luke Huan Univ. of Kansas
Administrative
Histogram of quiz scores
9/17/2018
Luke Huan Univ. of Kansas

3. Luke Huan Univ. of Kansas
Review
Relational algebra
Use temporary variable
Use foreign key to join relations
A comparison is to identify a relationship
Use minus in non-monotonic operations
9/17/2018
Luke Huan Univ. of Kansas

4. Luke Huan Univ. of Kansas
Today’s Topic
Logical database design: Translation ER to relation schema
9/17/2018
Luke Huan Univ. of Kansas

5. Luke Huan Univ. of Kansas
Database Design
9/17/2018
Luke Huan Univ. of Kansas

6. Database design steps: review
Understand the mini-world
Specify it using a database design model (e.g., E/R)
Translate specification to the data model of DBMS (e.g., relational)
Create DBMS schema
Next: translating E/R design to relational schema
9/17/2018
Luke Huan Univ. of Kansas

7. Luke Huan Univ. of Kansas
E/R model: review
Entity sets
Keys
Weak entity sets
Relationship sets
Attributes on relationships
Multiplicity
Roles
Binary versus N-ary relationships
Modeling N-ary relationships with weak entity sets and binary relationships
9/17/2018
Luke Huan Univ. of Kansas

8. Translating entity sets
An entity set translates directly to a table
Attributes ! columns
Key attributes ! Primary key
Students
Courses
CID
title
Enroll
SID
name
grade
Student (SID, name)
Course (CID, title)
9/17/2018
Luke Huan Univ. of Kansas

9. Translating entity sets (cont.)
Notes:
No multi-valued attributes (called first Normal Form)
Composite attributes is broken down into a list of atomic attributes
9/17/2018
Luke Huan Univ. of Kansas

10. Translating weak entity sets
Use a “borrowed” key
Watch out for attribute name conflicts
number
name In
Rooms
Buildings
capacity
year In
Seats
number
L/R?
Building (building_name, year)
Rooms (building_name, room_number, capacity)
Seats (building_name, room_number, seat_number, left_or_right)
9/17/2018
Luke Huan Univ. of Kansas

11. Translating 1:1 Relationship
Translate a 1:1 relationship between two entities.
Merging the two entity types and the relationship into a single table.
Works well for total participation
Students
account
aid
date
own
SID
name
Student (SID, name, aid, date)
9/17/2018
Luke Huan Univ. of Kansas

12. Translating 1:1 Relationship (II)
Mapping 1:1 relationship using foreign key
Usually choose the entity type with total participation to include the foreign key (why?)
Students
Bschool account
Baid
date
own
SID
name
Student (SID, name)
Bschoool account (Baid, SID, date)
9/17/2018
Luke Huan Univ. of Kansas

13. Translating 1:1 Relationship (III)
Mapping 1:1 relationship using relation
Termed as relationship relation
SID
Baid
own
Students
Bschool account
name
date
Bschoool account (Baid, date)
Student (SID, name)
Saccount(SID, Baid)
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Luke Huan Univ. of Kansas

14. Translating 1:N Relationship
Mapping 1:N relationship using foreign key
Or using relationship relation
EID
Dnum
worksfor
Employee
Department
name
Manager
Employee (EID, name, Dnum) Department(Dnum, Manager)
Employee (EID, name), Department(Dnum, Manager)
workFor(Eid, Dnum),
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Luke Huan Univ. of Kansas

15. Translating M:N Relationship
Use relationship relation
EID
Pnum
workson
Employee
Project
name
Budget
Employee (EID, name), Project(Pnum, Budget)
workon(Eid, Pnum),
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Luke Huan Univ. of Kansas

16. Mapping of Multivalued attributes.
Mapping multivalued attribute using relation.
Use primary key attribute from the original entity as a foreign key in the new relation
Dnum
Department
location
Manager
Department(Dnum, Manager)
DepartmentLocation(Dnum, location)
9/17/2018
Luke Huan Univ. of Kansas

17. Mapping of N-ary relationship
For each n-ary (n>2) relationship type, create a new relationship relation S.
Include as foreign key attributes in S the primary keys of the relations that represent the participating entity types.
Supply
Supplier
Project
Part
PID
Mname
SID
name
PaID
Pname
Supply(SID, PID, PaID)
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Luke Huan Univ. of Kansas

18. Luke Huan Univ. of Kansas
More examples
Persons
Marry
husband
wife
SSN
Marry (husband_SSN, wife_SSN)
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Luke Huan Univ. of Kansas

19. Luke Huan Univ. of Kansas
Design principles
KISS
Keep It Simple, Stupid
Avoid redundancy
Redundancy wastes space, complicates updates and deletes, promotes inconsistency
Capture essential constraints, but don’t introduce unnecessary restrictions
Use your common sense
Warning: Mechanical translation procedures given in this lecture are no substitute for your own judgment
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Luke Huan Univ. of Kansas

20. Luke Huan Univ. of Kansas
Review
Entity
Weak-entity
1:1 relationship
1:N relationship
M:N relationship
Atomic attribute
Key attribute
Composite attributes
Multi-valued attributes
Relation
Relation, including the primary key from the parent
entity as an attribute
Merged relation, Foreign key, Relationship relation
Foreign key, Relationship relation
Relationship relation
Attribute
Primary key
A set of attributes
Relation and foreign key
9/17/2018
Luke Huan Univ. of Kansas