How to unzip a zipped XML file on iPhone?

Question

I am developing an application in which I get a zip XML file from a web service. Now I need to unzip it, and I have to parse it. How can I unzip an XML file from a web service ??? Do I need to save the unpacked file (after unpacking) before taking it for analysis or is there code that gives the unpacked file directly without saving it in the document directory?

The code for this is useful.

Thanks in advance.