 What is an Entity-Relationship Diagram? An entity-relationship diagram (ERD) is a snapshot of data structures. ERDs show entities in a database and relationships between tables within that database. It is essential to have one of these if you want to create a good database design.

 What are the symbols used in ERD? The symbols are: Entity which is the source or destination of data, represented by a rectangular shape.

Relationship which shows the relation between the entities, represented by a diamond shape.

Attribute, which shows the things that falls between the entity and relationship, that is what make them relate. This is represented by a circular shape.

 What is one-one relationship? A one-one relationship is where one instance of an entity(A) is associated with one other instance of another entity(B). For example, in a database of employees, each employee name(A) is associated with only one social security number(B).

 What is a one-many relationship? A one-many relationship is where one instance of an entity(A) is associated with zero, one or many instances of another entity (B), but for one instance of entity B there is only one instance of entity A. for example, for a company with all employees working in one building, the building name(A) is associated with many different employees(B), but those employees all share the same singular association with entity A.

 What is a many-many relationship? A many-many relationship is where one instance of an entity(A) is associated with one, zero or many instances of another entity(B), and one instance of entity B is associated with one, zero or many instances of entity A. For example, for a company in which all of its employees work on multiple projects(B), and at the same time, each instance of a project (B) has multiple employees(A) associated with it. Presentation done by Faithlyn McCalla