Here is a screen shots example of exporting Purchase Header and relative tables (Vendor and Item). At the end of example you can open and see an example of generated xml file.
ExchObject 50101 (Purchase Header table)
ExchObject 50102 (Vendor table)
ExchObject 50103 (Purchase Line table)
ExchObject 50104 (Item table)
On this link you can see what xml file is generated XML file output
Some screen shots of import adjustment
Fields mapping sample
Import ExchObject Sample (Purchase Header table)