E-R Diagrams

E-R diagrams are graphical representation of the data modeling. E-R diagrams helps in defining the relationship between different entities. ER diagrams uses symbols to represent three different types of information. The symbols are,

Rectangular boxes are used to represent entities. Diamonds are normally used to represent relationships and ovals are used to represent attributes.

Entity

A data entity is anything in real or abstract about which user want to store data. e.g., worker, payment, book, etc.

Relationship

A relationship is an association that exists between one or more than one entities. e.g.,”the customer places an order”, here in this example places defines the relationship between customer and the order that customer place.

Attribute

Attributes are the characteristics which are common to all or most instances of a particular entity.e.g. Name, address, Phone number, Employee ID,etc are all attributes of the entity employee. An attribute which uniquely identifies one and only one instance of an entity is called a primary key. Primary key can be combination of attributes. E.g. Employee ID is a primary key for Employee.

An example E-R diagram is illustrated below, which is between movie,theatre, show,actor and screen.