My last lecture was all about the Entity Relationship Model.
In software engineering, an entity–relationship model (ER model) is a data model for describing the data or information aspects of a business domain. A graphical representation of entities and their relationships to each other, used in computing in regard to the organisation of data within databases or information systems.An entity is a piece of data, an object or concept about which data is stored.
An ERD typically consists of four different graphical components:
There are three different types of ERD’s:
This diagram demonstrates examples for each type of ERD.
For a binary relationship set the mapping cardinality must be one of the following types:
One to One – A husband and wife
One to Many – A football team with many footballers
Many to Many – Lots of students studying lots of different subject.