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Entity Relationship Diagrams

Entity Relationship Diagrams. Entity. “An entity is a business object that represents a group, or category of data.” 1 Do we know a similar concept? . 1) Stephens, R.K. and Plew. R.R., 2001. Database Design . SAMS, Indianapolis , IN. Attribute.

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Entity Relationship Diagrams

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  1. Entity Relationship Diagrams

  2. Entity • “An entity is a business object that represents a group, or category of data.”1 • Do we know a similar concept? 1) Stephens, R.K. and Plew. R.R., 2001. Database Design. SAMS, Indianapolis , IN.

  3. Attribute • “An attribute is a sub-group of information within an entity.”1 • Do we know a similar concept? 1) Stephens, R.K. and Plew. R.R., 2001. Database Design. SAMS, Indianapolis , IN.

  4. Entity Relationship Models • Mandatory Relationships • Optional Relationships • Many-to-Many Relationships • One-to-Many Relationships • One-to-One Relationships • Recursive Relationships

  5. INSTRUCTOR STUDENT INSTRUCTOR STUDENT Mandatory, Many-to-Many

  6. DEPARTMENT STUDENT DEPARTMENT STUDENT Optional, Many-to-Many

  7. INSTRUCTOR SKILL INSTRUCTOR SKILL Optional/Mandatory,Many-to-Many

  8. PRODUCT VENDOR PRODUCT VENDOR Optional/Mandatory,One-to-Many

  9. AUTOMOBILE ENGINE AUTOMOBILE ENGINE Mandatory, One-to-One

  10. Recursive EMPLOYEE supervises is supervised by

  11. Resolving Many-to-Many Relationships • Many-to-many relationships should be avoided. We can resolve a many-to-many relationship by dividing it into two one-to-many relationships.

  12. SALES ORDERS INV. ITEMS SALES ORDERS ORDER ITEMS INV. ITEMS Resolving Many-to-Many Relationships

  13. CUSTOMERS CLERKS SALES ORDERS ORDER ITEMS INV. ITEMS Example (ER Diagram)

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