A very NEWBIE question

Hi,
   There is the "class" in ontology, and there is also the "class" in
OO(Object Oriented). I think they are completely different because they
are different domain concept. But "class and individual" in ontology and
"class and individual" in OO, what's the difference between them? 
   I think:
   1. The individual in OO is of a certain class, if you want to extend
it, you must overload or cast a new class to it. But individual in
ontology you must do a "Realization" job to know what class it is of
through a reasoner.
   2. If you want to add a new property, you must modify the class in
OO, but you needn't modify the class in ontology, you can just set the
property's domain and range to add it.
   So I think the class and the individual is much more extendable in
ontology than in OO.
   And what are other differences?
   
   Thank all.

Best regards,
Zhu Bin