INHERITANCE

• IMPLEMENTATION HIERARCHY: FOR CODE SHARING BETWEEN CLASSES (OR TYPES)
  
  
  • CLASS CAN BE IMPLEMENTED BY DIFFERENCE FROM ANOTHER CLASS
  • INHERITED ATTRIBUTES & METHODS CAN BE FREELY MODIFIED
  
  
• CLASSIFICATION HIERARCHY: DESCRIBES COLLECTIONS OF OBJECTS AND THEIR INCLUSION RELATIONSHIP

• IN ODBMSs RESTRICTIONS TO THE MODIFICATION OF OBJECT'S STRUCTURE (IN AN IMPLEMENTATION HIERARCHY) ARE SOMETIMES NECESSARY TO INSURE THAT THE OPERATION OF QUERIES ON THE INSTANCES OF CLASSES IN THE HIERARCHY REMAIN WELL DEFINED
  
  
  • SUCH RESTRICTION CAN APPLY EVEN IF THE ATTRIBUTES ARE NOT VISIBLE
  
  

Previous: Page 18 Next: Page 20 Up A Level: Inheritance

Ugo O. Gagliardi
GSD-6306 Spring 2003-2004