Some Patterns

• 1:N
  • 
  • The company has many departments.
  • We need to ask
    • Can a company exist if there are no departments? (In this case yes)
    • Can a department exist in several companies (No)
    • Can a department exist with no company? (No)
  • This is one to many , mandatory to optional.
  • 
• N:M
  • 
  • Notice that a company has many parts from the form.
  • Notice also that a part is supplied by many companies from the report
  • So this is clearly an N:M relationship.
  • Not all companies we deal with are suppliers, so a company is not required to have a part. (Optional)
  • But a part must come from somewhere (required)
  • 
• ID Dependent
  • Association pattern
    • The Part report is supplemented with the Part Quotation Report
    • 
    • Notice the addition of a quoted price.
    • This price is not part of the company
    • It is not part of the part (Different companies supply the same part_
    • A new entity is required.
    • 
    • They give another example
      • a Client exists in a firm
      • Each Client may have one or more projects
      • An architect may be assigned to one or more projects
      • So an Assignment is made which matches Clients to Projects to Architects.
      • 
  • Multivalued Attribute Pattern
    • 
    • Here a company has multiple phone numbers.
    • 
    • How does this change things?
    • 
    • How about this?
    • 
  • Archetype/Instance Pattern
    • An entity represents an instance of another entity
    • Consider a university
      • There is a catalog of courses
      • There is a schedule of courses offered.
      • 
• Mixed Identifying and Nonidentfying Patterns
  • Line Item
    • 
    • We have a salesperson
    • A customer
    • An order connects both.
    • But the order is made up of line-items
    • Which connects it to an item.
    •