db import from some external xml data

Hi , i'm looking for db import from external xml file , which method
is usual for this process , should i create new xml file (using rexml)
for arrange them or import directly to my db . i'll work about 4 or 5
external xml data (every xml file has different xml scheme) and
integrate(create new , delete or update price of existing one ) every
3 hours in my db then show in my site.
Thanks for your suggestions.