最病 E Schema evolution 口Fact: Classes change a Problem: Objects are stored of which class descriptions have changed a Schema evolution: o At least one class used by the retrieving system differs from its counterpart stored by the storing system o Object retrieval mismatch(object mismatch a The retrieving system retrieves a particular object whose own generating class was different in the storing system a No fully satisfactory solution Institute of Computer Software 2021/1/28 Nanjing UniversitySchema evolution  Fact: Classes change  Problem: Objects are stored of which class descriptions have changed  Schema evolution:  At least one class used by the retrieving system differs from its counterpart stored by the storing system.  Object retrieval mismatch (Object mismatch):  The retrieving system retrieves a particular object whose own generating class was different in the storing system.  No fully satisfactory solution 2021/1/28 Institute of Computer Software Nanjing University 47