Translating business requirements to Entity Relationship Diagrams (ERDs)

What is an ERD?

An Entity Relationship Diagram, or ERD is a schematic model of the data requirements for a database. An ERD does not focus on implementation.

ERD Objects:

Entity, such as product, employee, customer, or film. In SQL an entity is a TABLE.

Relationship describes the “link” between entities, for example customer buys product. In SQL a relation is a foreign key.

Attribute is an attribute of the entity, such as product ID. In SQL an attribute, or field, is a COLUMN of the TABLE.

In an ERD entities are rectangles, relationships are lines between the rectangle, and attributes are added inside the rectangles.

An ERD is usually accompanied by a Data Dictionary, which defines the names and descriptions of ERD objects in text format.

An instance is a specific statement about specific entities, as for example. “Student Janelle Adams registers for CS 100 Section 02 with Instructor Ana Davis.” Therefore, an entity can have multiple instances.

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