Techniques are disclosed for serializing objects (such as Java.TM. objects), and deserializing those objects, in a manner that enables contents of the objects to be preserved following changes to definitions of the object structures. Objects are serialized using documents encoded in a markup language (such as Extensible Markup Language, or "XML"). The serialized objects thereby capture class definition information for the class definition which was in effect when the object was serialized. Subsequently, if the class definition is changed, techniques disclosed herein enable deserializing the information from the markup language document to an object that uses the new class definition, without requiring access to a programming language specification of the now-obsolete class definition.