OPatch was not able to get details of the home from the inventory

If OPatch is failing becuase of inventory issues, you can force it to use the inventory you have. Try to use this:
-opatch apply -invPtrLoc

Server Level and Application Level Configuration Files in OAS

I was editing, using, sometimes digging these files but it is really useful to have them all listed like this.
I found it really useful especially when you knew to edit this xml file but not sure where it was or how to do it.
Here is the documentation from Oracle Technology Network Documentation:
http://download.oracle.com/docs/cd/E12524_01/web.1013/e12288/confdesc.htm
Enjoy!