I am pretty new to ios and using servers so forgive me.

I am building an ios app for research. I need to monitor things that the user does and then push it up to a server for analysis (yes, with user and IRB permission). On the client's side I need to keep quite a bit of data that won't really change except in the case of pulling an updated version from the server, and then a minimal amount of user-specific data. Most of the data I will collect needs to be pushed to a server for analysis and then can be deleted from the client side.

I am struggling to figure out what kind of data store I need to use, especially since I am not quite sure how the pushing and pulling from the server process works yet. Does it make sense to use Core Data? XML? SQLite? I like the Core Data idea, but I am not sure what kind of problems I will run into when I need to send large amounts of data to it and from it from the server. I imagine I might need to send data in a different form than it is probably stored in on either end - so what kind of overhead am I likely to run into in the process of converting that data? Is there a good format to save stuff in that would work well for me on both ends AND for sending the data?

As you can probably tell, I could use some advice. Thanks!