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 .
- 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
- 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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