1. CSCI-100 Introduction to Computing
Databases
Part II

2. Database Models Define the way a database organizes data
Four main models
Hierarchical
Network
Relational
Object-oriented

3. Relational Database Each entity is stored in a separate table
Columns represent fields
Rows represent records
Tables are linked by a relationship between primary and foreign keys

4. Integrity Constraints
Define acceptable values for a field
For example, the value of a month cannot be greater than 12
Primary keys cannot be duplicated
Foreign keys cannot be used unless they exist as a primary key
A SalesID that is used in the customer table must exist as a primary key in the salesperson table

5. Primary Key Foreign Key A field that uniquely identifies a record
SalesID can be a primary key for the SalesPerson table
Once a SalesID appears in the table, no other salesperson can have that ID
Foreign Key
A field in one table that is a primary key in another table
SalesID can be used in the Customer table to identify the salesperson who serves that customer
The same SalesID can appear in many customer records (a salesperson can serve many customers)

6. Entity-Relationship (ER) Diagram
The logical structure of a database can be expressed
graphically by an ER diagram. Such a diagram consists
of some major components
Rectangles, which represent entities
Ellipses, which represent attributes
Diamonds, which represent relationships
Lines, which link attributes to entities and entities to relationships
EXAMPLE: ER diagram for a bank
(DONE IN CLASS)

7. A database that conforms to an ER diagram can be
represented by a collection of tables
Converting an ER diagram to a table format is the basis
for deriving a relational database from and ER diagram
design
EXAMPLE: Relational database from bank ER diagram
(DONE IN CLASS)