1 / 13

Entity-relationship diag rams a nd generation

Entity-relationship diag rams a nd generation. Jozef Kuper. ERD. Describe a Database Entities Atributes Relationships. ERD – Entity and atributes. Physical object, concept or event Entity represent table Attributes represent collums Primary key. ERD - Relationships.

ama
Download Presentation

Entity-relationship diag rams a nd generation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Entity-relationship diagramsand generation Jozef Kuper

  2. ERD • Describe a Database • Entities • Atributes • Relationships

  3. ERD – Entity and atributes • Physical object, concept or event • Entity represent table • Attributes represent collums • Primary key

  4. ERD - Relationships • Represented as a lines between entities • May be labeled • Don’t show single instance of relations • Entity sets • Relationships sets • Optional relationship • Mandatory relationship

  5. Cardinality • One-to-one • One-to-many • Many-to-many

  6. Levels of ER model • Conceptual data model • Useful to support documenting the data architecture • Logical data model • Physical model

  7. One-to-one • Unusual • Used in large tables • Safety

  8. Many-to-one • Most used • Relationship 1:N | N:1 • Primary key / Foreign key • Classifications

  9. Many-to-many • Can not be implemented • Generated associated entity • Combination of entity and relationship

  10. Recursive relation • Some entity participates more than once in the relationship • Some common attributes • <Employee>reports to<Employee>(manager)

  11. How to create ERD • Identify the entity • Identify the entity’s attribute • Identify Primary Keys • Identify relations between entities • Identify the Cardinality constraint

  12. Example

  13. Thanks for your attention Questions?

More Related