Entity-relationship diagrams

and generation

Jozef Kuper

Describe a Database Entities Atributes Relationships

ERD

Physical object, concept or event Entity represent table Attributes represent collums Primary key

ERD – Entity and atributes

Represented as a lines between entities May be labeled Don’t show single instance of relations Entity sets Relationships sets Optional relationship Mandatory relationship

ERD - Relationships

One-to-one One-to-many Many-to-many

Cardinality

Conceptual data model Useful to support documenting the data

architecture Logical data model Physical model

Levels of ER model

Unusual Used in large tables Safety

One-to-one

Most used Relationship 1:N | N:1 Primary key / Foreign key Classifications

Many-to-one

Can not be implemented Generated associated entity Combination of entity and relationship

Many-to-many

Some entity participates more than once in the relationship

Some common attributes <Employee>reports

to<Employee>(manager)

Recursive relation

Identify the entity Identify the entity’s attribute Identify Primary Keys Identify relations between entities Identify the Cardinality constraint

How to create ERD

Example

Thanks for your attention

Questions?