hello all , I am developing Iphone app that reads data from url and after parsing i should save that data for persistance.(Because of getting app in offline also...). I want to use core data for this. Such that first time only we will read the data from url and save into objct model, so from second time onwards we can fetch the data from core data store and dispaly to the user. now what my problem is how to maintain primary and foreign key relations in the entities and how to create entities programitacally .. Thanks all