protected void makeSets() {
		people = new HashSet<Person>();
		families = new HashSet<Family>();
		notes = new HashSet<Note>();
		sources = new HashSet<Source>();

		for (Iterator iter = xrefTable.values().iterator(); iter.hasNext();) {
			Core o = (Core) iter.next();

			if (o instanceof Person)
				people.add((Person)o);
			else if (o instanceof Family)
				families.add((Family)o);
			else if (o instanceof Note)
				notes.add((Note)o);
			else if (o instanceof Source)
				sources.add((Source)o);
		}
	}