Published on 27 Nov 2013 | over 3 years ago
Entity-Relationship Diagram Tutorial
An Entity-Relationship diagram (ERD) typically serves as the main deliverable of a conceptual data model. While newer approaches to E-R modeling have developed, the E-R approach is still cited by some professionals as "the premier model for conceptual database design". An ERD is a logical representation of an organization's data, and consists of three primary components:
Entities -- Major categories of data and are represented by rectangles
Attributes -- Characteristics of entities and are listed within entity rectangles
Relationships -- Business relationships between entities and are represented by lines
An Entity is a person, place, object, event, or concept that an organization wants to maintain data on. Each entity has a unique identity that differentiates it from other entities. A point of distinction must be made between entity types and entity instances. An entity type is a collection of entities that share common properties. Entity types are also known as entity classes. An entity instance is an individual occurrence of an entity type. A data model describes an entity type only once; however there may be numerous instances of that type within a database.