Newsgroups: comp.lang.c++
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!caen!ox.com!hela!widener!news.cs.indiana.edu!nstn.ns.ca!cs.dal.ca!ug.cs.dal.ca!kelly
From: kelly@ug.cs.dal.ca (Michael Kelly)
Subject: Retrieving Objects?
Message-ID: <1991Apr12.154547.9732@cs.dal.ca>
Sender: news@cs.dal.ca (USENET News)
Nntp-Posting-Host: ug.cs.dal.ca
Organization: Math, Stats & CS, Dalhousie University, Halifax, NS, Canada
Distribution: dal
Date: Fri, 12 Apr 91 15:45:47 GMT

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.