E-R diagram in Database
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An E-R diagram is a logical representation of data in an organization that views the entire system as entities related to one another. The key elements of an E-R diagram are entities, attributes, and relationships. Entities represent people, places, things, or events and have attributes with defined domains. Relationships connect different entities and can be one-to-one, one-to-many, or many-to-many. E-R diagrams were introduced in 1976 and provide advantages like a logical structure for modeling an organization's data.
E-R diagram in Database
- 1. E-R Diagram
- 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. Advantages of E-R Model:
- 5. Elements of E-R Model: 1: Entities 2: Attributes 3: Relationships
- 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. 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. Entity instance A member of an entity class is known as entity instance . Also known as entity occurrence.
- 11. Example: Name, address,Class and Email of a students are his attributes. Attribute name Symbol
- 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. *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. Doctor treats Patient Teacher teaches students
- 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.
- 17. 1: Simple 2: composite 3: single valued 4: multi-valued 5: stored 6: derived 7: identifiers
- 18. *Cannot be subdivided into smaller components. PERSON GENDER
- 19. *Can be divided into smaller components. EMPLOYEE ADDRESS street city country
- 20. Single-valued Attributes: Contain single valued value. Employee Gender Multi-valued Attributes: Contain two or more values. person name city hobies
- 21. *Stored in a database. *Not stored in database but derived from another value.
- 22. Identifies an entity instance among other instances In entity class.
- 24. 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
- 25. Type of entity that associates the instances of one or many entity type with one another.
- 26. •The number of entities in a relationship . •Types: •1: unary relationship •2: binary relationship •3: ternary relationship
- 28. Exist between the instances of two entity types. Types: 1: one-to-one 2:one-to-many 3:many –to-many
- 31. The maximum number of relationships.
- 32. *Circle means zero *Line means………..one *Crow’s foot symbol means….many
- 35. name DOB Phone no Project no Project name Project cost duration name Address Date of last meeting number