An entity relationship diagram (ERD), also known as an entity relationship model, is a graphical representation that depicts relationships among people, objects, places, concepts or events within an information technology (IT) system. An ERD uses data modeling techniques that can help define business processes and serve as the foundation for a relational database. Show
Importance of ERDs and their usesEntity relationship diagrams provide a visual starting point for database design that can also be used to help determine information system requirements throughout an organization. After a relational database is rolled out, an ERD can still serve as a reference point, should any debugging or business process re-engineering be needed later. However, while an ERD can be useful for organizing data that can be represented by a relational structure, it can't sufficiently represent semi-structured or unstructured data. It's also unlikely to be helpful on its own in integrating data into a pre-existing information system. How to create an ERDERDs are generally depicted in one or more of the following models:
There are five basic components of an entity relationship diagram. Similar components will be designated by the same shape. For example, all entities types might be enclosed in a rectangle, while all attributes are enclosed in a diamond. The components include:
For example, an ERD representing the information system for a company's sales department might start with graphical representations of entities such as the sales representative, the customer, the customer's address, the customer's order, the product and the warehouse. (See diagram above.) Then lines or other symbols can be used to represent the relationship between entities, and text can be used to label the relationships. A cardinality notation can then define the attributes of the relationship between the entities. Cardinalities can denote that an entity is optional (for example, a sales rep could have no customers or could have many) or mandatory (for example, there must be at least one product listed in an order.) The three main cardinalities are:
While there are tools to help draw entity relationship diagrams, such as computer-aided software engineering (CASE) tools, some relational database management systems (RDBMS) also have design capabilities built in. This was last updated in September 2019 Continue Reading About Entity Relationship Diagram (ERD)
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