private Map<Class<?>, Set<Class<?>>> buildDirectOwnedToOwnerdMap() {
        Map<Class<?>, Set<Class<?>>> clsToOwnersMap = new HashMap<>();
        
        for (Class<?> ownerCls : ownerToOwnedMap.keySet()) {
            Map<String, Class<?>> ownedMap = ownerToOwnedMap.get(ownerCls);
            for (Class<?> ownedCls : ownedMap.values()) {
                CommonUtil.addToSetMap(clsToOwnersMap, ownedCls, ownerCls);
            }
        }
        
        return clsToOwnersMap;
    }