Accessing files in iPhone

I am developing an application in iOS 4.0, after having made several apps in Symbian S60v3. Where I am stuck in iOS is that I want to access a file from the device which is saved from a third-party application开发者_如何学运维 to some location on the device.

In the case of symbian I knew its location: System\Data\xyz\alpha.inf, but with iOS I don't know how to access the location.

You can't. It is one of the security features in iOS that applications are sandboxed and cannot share data at all.