public Descriptor descriptorFor(String ident) {
	    // built-in types
	    if (("integer").equalsIgnoreCase(ident)) {
	        return new SimpleTypeDescriptor(Type.INTEGER);
	    }else if(("string").equalsIgnoreCase(ident)){
	        return new SimpleTypeDescriptor(Type.STRING);
	    }else if(("boolean").equalsIgnoreCase(ident)){
	        return new SimpleTypeDescriptor(Type.BOOLEAN);
	    }
	    Descriptor d = descriptorMap.get(ident);
		if(d == null && parentTable != null){
			return parentTable.descriptorFor(ident);
		}else if(d == null){
			error("Deskriptor fuer " + ident + " nicht gefunden.");
		}
		return d;
	}