E R Diagram

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E R Diagram

  1. 1. Entity Relationship Diagrams
  2. 2. Entity <ul><li>“An entity is a business object that represents a group, or category of data.” 1 </li></ul><ul><li>Do we know a similar concept? </li></ul>1) Stephens, R.K. and Plew. R.R., 2001. Database Design . SAMS, Indianapolis , IN.
  3. 3. Attribute <ul><li>“An attribute is a sub-group of information within an entity.” 1 </li></ul><ul><li>Do we know a similar concept? </li></ul>1) Stephens, R.K. and Plew. R.R., 2001. Database Design . SAMS, Indianapolis , IN.
  4. 4. Entity Relationship Models <ul><li>Mandatory Relationships </li></ul><ul><li>Optional Relationships </li></ul><ul><li>Many-to-Many Relationships </li></ul><ul><li>One-to-Many Relationships </li></ul><ul><li>One-to-One Relationships </li></ul><ul><li>Recursive Relationships </li></ul>
  5. 5. Mandatory, Many-to-Many INSTRUCTOR STUDENT INSTRUCTOR STUDENT
  6. 6. Optional, Many-to-Many DEPARTMENT STUDENT DEPARTMENT STUDENT
  7. 7. Optional/Mandatory, Many-to-Many INSTRUCTOR SKILL INSTRUCTOR SKILL
  8. 8. Optional/Mandatory, One-to-Many PRODUCT VENDOR PRODUCT VENDOR
  9. 9. Mandatory, One-to-One AUTOMOBILE ENGINE AUTOMOBILE ENGINE
  10. 10. Recursive EMPLOYEE supervises is supervised by
  11. 11. Resolving Many-to-Many Relationships <ul><li>Many-to-many relationships should be avoided. We can resolve a many-to-many relationship by dividing it into two one-to-many relationships. </li></ul>
  12. 12. Resolving Many-to-Many Relationships SALES ORDERS INV. ITEMS SALES ORDERS INV. ITEMS ORDER ITEMS
  13. 13. Example (ER Diagram) SALES ORDERS INV. ITEMS ORDER ITEMS CLERKS CUSTOMERS

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