what is entity-relationship diagram ?

An entity-relationship diagram, or ERD, is a chart that visually represents the relationship between database entities. ERDs model an organization’s data storage requirements with three main components: entities, attributes, and relationships.

  • As noted above, there are 3 ingredients in a standard entity-relationship diagram:
  • Entities, which represent people, places, items, events, or concepts.
  • Attributes, which represent properties or descriptive qualities of an entity. These are also known as data elements.
  • Relationships, which represent the link between different entities.
  • ERD act as blueprint for database design
  • In software design how UML diagram plays vital role for defining a system,ER diagram plays very vital role designing data base .

ERD

  • let as assume Entities are the tables and rows in the tables are know instances of that table
  • A Database is nothing but organization collection of data which is used for data store and interviewing and its nothing but bunch of data interlinked with each other.
  • Cardinality tells us how many rows from the table should be taken or considers linking other table
  • Cardinality is broken into two parts
  • Minimum and
  • Maximum
  • Minimum Cardinality means minimum number of instances that are required in a relationship
  • Maximum Cardinality means Maximum number of instances that are required in a relationship
  • They are four different ways to represent the Cardinality
  • One Mandatory
  • One Optional
  • Many Mandatory
  • Many Optional
  • Key Attributes
  • Multi Value Attitude-
  • Derived Attribute-Represent with Dotted Circle

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