1. Day 2 - Basic Database Backbone
How to Model a Database Using E/R Diagrams
How an E/R Diagram Translates to a Real Database

2. How do I model a database?
Why do I need to model a system?
Gives a team a basis to design a system on.
Design Issues
Entity Designs and Relationships
Domain/Range Constraints of the System
Good Entity Relationship Design
Entity/Relationship Model
Used to model the relationships between different objects in the database.
Parallel structure to an object-oriented approach of thinking.
CSE 498
Day 2 - Basic Database Backbone

3. Day 2 - Basic Database Backbone
E/R Diagram Parts
Entities
Attributes & Keys
Relationships
Entity
Major objects in a database.
Strong Entity: Records are uniquely identified by its attribute(s).
Weak Entity: Records are uniquely identified by its relationship(s). Weak entities are shown with double borders around the entity block.
Customers
Customers
CSE 498
Day 2 - Basic Database Backbone

4. Day 2 - Basic Database Backbone
Attributes & Keys
Attribute
A piece of information that defines a part of the entity.
Drawn as ovals that link off an entity.
Example:
LastName
Customers
FirstName
CustID
Age
Address
Key
Attribute(s) that uniquely identify an entity.
Drawn by underlining the attribute name in the E/R diagram.
Example shown above.
CSE 498
Day 2 - Basic Database Backbone

5. Day 2 - Basic Database Backbone
Relationships
Relationship
Diagram definition of how entities relate to each other.
Drawn as a line between two objects with a diamond defining the relationship. An arrow defines the direction of the relationship.
Weak relationships are drawn as double lines.
Three types of relationships…
1 to 1 (One To One)
N to 1 (Many To One)
N to M (Many To Many)
Rented By
Rented By
Rented By
CSE 498
Day 2 - Basic Database Backbone

6. Example Simple Movie DB
Customers
CustID
LastName
FirstName
Address
CatID
CatName
Age
Category
In Category
MovieID
Rented By
Title
Rentals
CopyNum
Movie Rented
CheckOut
Duration
Cost
CheckOutDate
CSE 498
Day 2 - Basic Database Backbone

7. How does an E/R translate to a DB?
All entities become tables.
All attributes become columns in the tables.
Relationships are tricky…
One-To-One and Many-To-One relationships are handled by adding in the keys from the higher level table to the lower level table.
Many-To-Many relationships are handled by creating a table that has the keys from both entities to define the different relations.
CSE 498
Day 2 - Basic Database Backbone

8. Movie E/R Diagram Translated to a DB
Customer
CustID (integer) -- Key
LastName (VarChar)
FirstName (VarChar)
Address (VarChar)
Age (int)
CheckOut
CustID (integer) -- Key
MovieID (integer) -- Key
CheckOutDate (Date/Time)
Duration (integer)
Cost (Money)
Category
CatID (integer) -- Key
CatName (VarChar)
Rentals
MovieID (integer) -- Key
Title (VarChar)
CopyNum (integer)
CatID (integer)
CSE 498
Day 2 - Basic Database Backbone