kelly@ug.cs.dal.ca (Michael Kelly) (04/12/91)
This is really a two part question: 1) if PERSON is a class and EMPLOYEE is a subclass of PERSON and TOM is an instance of EMPLOYEE then TOM is a PERSON right? 2) ok, now assuming TOM is a PERSON, but is really an instance of EMPLOYEE, how is TOM stored so that when I ask for all instances of PERSON I will get TOM? ie. is TOM's object ID somehow associated with the class PERSON? I am looking for an answer in terms of persistent storage, ie. if I want to save the state of the system to disk and then retrieve bits and pieces later how will I know TOM is a PERSON and an EMPLOYEE without retrieving everything in the class hierarchy? Please e-mail any help, kelly@ug.cs.dal.ca PS. Please excuse any obvious demonstrations of ignorance.
kelly@ug.cs.dal.ca (Michael Kelly) (04/12/91)
This is really a two part question: 1) if PERSON is a class and EMPLOYEE is a subclass of PERSON and TOM is an instance of EMPLOYEE then TOM is a PERSON right? 2) ok, now assuming TOM is a PERSON, but is really an instance of EMPLOYEE, how is TOM stored so that when I ask for all instances of PERSON I will get TOM? ie. is TOM's object ID somehow associated with the class PERSON? I am looking for an answer in terms of persistent object storage. ie. how is TOM represented if I save my system to disk such that I can retrieve the object TOM and know it is a PERSON and an EMPLOYEE? Please e-mail any help, kelly@ug.cs.dal.ca PS. Please excuse any obvious demonstrations of ignorance.