namespace PersistentData
{
    public class UUIDGenerator : IIdentifierGenerator
    {
        public const int TYPE_PREFIX_LENGTH = 8;
        public const string PERSISTENT_OBJECT_PREFIX = "persistn";

        private static IDictionary<Type, string> _typeToPrefix = new Dictionary<Type, string>();
        private static IDictionary<string, Type> _prefixToType = new Dictionary<string, Type>();

        static UUIDGenerator()
        {
            _typeToPrefix[typeof(IPersistentObject)] = PERSISTENT_OBJECT_PREFIX;
            _prefixToType[PERSISTENT_OBJECT_PREFIX] = typeof(IPersistentObject);
        }

        public static void registerType(Type type, string prefix)
        {
            _typeToPrefix[type] = prefix;
            _prefixToType[prefix] = type;
        }

        public static Type getTypeByUUID(string uuid)
        {
            return _prefixToType[uuid.Substring(0, TYPE_PREFIX_LENGTH)];
        }

        public object Generate(ISessionImplementor session, object obj)
        {
            var type = obj.GetType();

            while (!_typeToPrefix.ContainsKey(type) || type != typeof(object))
            {
                type = type.BaseType;
            }

            return _typeToPrefix[type] + "-" + Guid.NewGuid();
        }
    }
}

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="PersistentData" namespace="PersistentData">
  <class name="IPersistentObject" table="TBL_PERSISTENT_OBJECTS" abstract="true" >
    <id name="uuid">
      <column name="UUID"/>
      <generator class="PersistentData.UUIDGenerator"/>
    </id>
  </class>
</hibernate-mapping>