Hello, i m fiddling with CoreData now, with bindings and such, and its quite interesting to have all done for you ( used to coding with much less help form IDE and frameworks...) Now my question is in regards to sqlite and the modeling tool. First of all i limited the type of storage to sqlite, so i m sure its that. Now i need to create a field in my entities that is autonumerical, which means it automatically increments itself on each insert , is this possible? how would i go about doing this? Because i m confused as to how this works, i have this set up : Client entity, with name, telephone and IdNumber. then i have a Bill entity which has : client ( relationship), date, control number now this works fine, with an interface i am able to add new clients and on another interface i m able to add new bills and list the clients etc.. the question is , how does Coredata manage the relationship? what exactly does he put in the client relationship on the Bill entity? there is no ID, nothing unique. What i 'd like is to be able to define certain fields as unique keys and even autonumeric. there is the "indexed" box, but i m still not sure about exactly what the means. well if you' ve gotten this far, thanks for reading, and hope you can clear this up for me. Charles.