Entity

Definition: - Entity is a thing in the real world with an independent existence. Entity is the basic component of ER diagram. An entity may be an object with a physical existence (for example a particular parson, car, house, or employee) or it may be an object with a conceptual existence (for example a company, job, or university course). The graphical representation of entity is a rectangle for example person and city both are the entities in above ER diagram.

Entity Relationship Diagram

Definition: An entity-relationship (ER) diagram is a specialized graphic or graphical representation of ER model that illustrates the interrelationships between entities in a database. ER diagrams often use symbols to represent three different types of information. Boxes are commonly used to represent entities. Diamonds are normally used to represent relationships and ovals are used to represent attributes of entity.

Entity Relationship Model

Definition: ER Model is a popular high level conceptual data model. ER model describes the data as entity relationships and attributes. The basic objects that the ER model represents are an entity and attributes. This model and its variations are frequently used for the conceptual design of database applications, and many database design tools employ its concepts. The diagrammatic notation of ER Model is known as ER Diagram.