ER DIAGRAM NOTATIONS | Readstall

ER DIAGRAM NOTATIONS

16-12-18 Gudditi Naganjaneyulu 0 comment

An ER  diagram model is typically implemented as a database in the case of relational database in the case of a relational database  in the case of a relational database ,which stores data in the tables ,every row of each table are instance of an entity

Er diagram notations are :

  1. Entity
  2. Attribute
  3. Relation ship
  4. Week entity
  5. Week relationship
  6. Multivalve attribute
  7. Key attribute
  8. Line
  9. Derive attribute

Entity:

An entity is an object or conceptabout which business user to store information

Entity

Attribute :

A derivedattribute is based on another attribute .

Attribute

Relationship:

It derives there relationship between entities . relation ship is represented using diamond symbol

Relationship

Week entity :

To connect a week entity with others ,you should use a weak relationship notations

week entity

Week relationship:

To connect a week relationship entity with others you should use a week relationship notations

week entity relationship

weak entity

Multi valued attributes

Multivalued attributes may contain more than one values

Eg : a personhaving housing more tha one one email

Key attributes

A key attributesis the unique ,distinguishing characteristics of the attributes

attribute

Line :

 A line is used to links the attributes

Eg :

student  

Derived attributes :

 Attributes that can be calculated based on other attributes .derived attributes are depicited by dashed ellipse

Eg : age can be derived from dos



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