Er diagram
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The document discusses entity relationship diagrams and their components. An entity represents a category of data, and an attribute contains a subgroup of information within an entity. Relationship types in ER diagrams include mandatory, optional, many-to-one, one-to-many, and recursive. Many-to-many relationships should be avoided by dividing them into two one-to-many relationships using a joining table. Examples of different relationship types and resolving many-to-many relationships are provided.
Er diagram
- 1. INFM 603 – Information Technology and Organizational Context Lecture 8 Entity Relationship Diagrams
- 2. 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. 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. 4 Entity Relationship Models • Mandatory Relationships • Optional Relationships • Many-to-Many Relationships • One-to-Many Relationships • One-to-One Relationships • Recursive Relationships
- 11. 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. 12 Resolving Many-to-Many Relationships SALES ORDERS INV. ITEMS SALES ORDERS INV. ITEMSORDER ITEMS
- 13. 13 Example (ER Diagram) SALES ORDERS INV. ITEMSORDER ITEMS CLERKSCUSTOMERS