E-R diagram in Database


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  • its awwwwwwwwwwwwwwwwwwwwwwwwwwwesome. thanks to Fathia Qureshi and Javeria Rafeeq, for making a complex topic easy and precise.
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E-R diagram in Database

  1. 1. E-R Diagram
  2. 2. Presented by: Fatiha Rashid Javeria Rafeeq
  3. 3. Logical representation of data in an organization. Views the entire system as a collection of entities related to one another. Introduced by peter chen in 1976.
  4. 4. Advantages of E-R Model:
  5. 5. Elements of E-R Model: 1: Entities 2: Attributes 3: Relationships
  6. 6. Entities: An Entity is a Person,Place,Thing or Event for which data is collected and maintained. •Represented by a rectangle Entity namesymbol
  7. 7. Entitytype/Entityclass: A set of entities with same attributes Exmaple: Student entity class is a set of All students. Book entity type is for all Books etc.
  8. 8. Entity instance A member of an entity class is known as entity instance . Also known as entity occurrence.
  9. 9. Entity Class Entity instance
  10. 10. Entity class Entity instance
  11. 11. Example: Name, address,Class and Email of a students are his attributes. Attribute name Symbol
  12. 12. Attribute Domain: *A set of possible values for an attribute *All atributes have domain Example : The domain for Grade point average (GPA) can be from 0 to 4.
  13. 13. *A logical connection between different enities. * Established on the basis of interaction between these entities. Participents: entities participating In a relationship are called participents. Relationship name
  14. 14. Doctor treats Patient Teacher teaches students
  15. 15. If all entities of that entity set may be participant in the relationship. Example: In supplier_part relationship,the relationship is total if every part is supplied by a supplier. If some of the entities of that entity set may be participant in the relationship. Example: If certain parts are available without a supplier.
  16. 16. 1: Simple 2: composite 3: single valued 4: multi-valued 5: stored 6: derived 7: identifiers
  17. 17. *Cannot be subdivided into smaller components. PERSON GENDER
  18. 18. *Can be divided into smaller components. EMPLOYEE ADDRESS street city country
  19. 19. Single-valued Attributes: Contain single valued value. Employee Gender Multi-valued Attributes: Contain two or more values. person name city hobies
  20. 20. *Stored in a database. *Not stored in database but derived from another value.
  21. 21. Identifies an entity instance among other instances In entity class.
  22. 22. week entity Can exist only if any other entity exist, also called child ,dependent . Strong entity Can exist without depending upon the existance of another entity . PERSON HAS CHILDCHILD Owner/ identifying owner: entity on which the weak entity depends.Example
  23. 23. Type of entity that associates the instances of one or many entity type with one another.
  24. 24. •The number of entities in a relationship . •Types: •1: unary relationship •2: binary relationship •3: ternary relationship
  25. 25. Exist between the instances of two entity types. Types: 1: one-to-one 2:one-to-many 3:many –to-many
  26. 26. The maximum number of relationships.
  27. 27. *Circle means zero *Line means………..one *Crow’s foot symbol means….many
  28. 28. employee department jobs equipment suppliers project
  29. 29. name DOB Phone no Project no Project name Project cost duration name Address Date of last meeting number
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