Question about XML parsing

Hi, 

I'm parsing an XML file, there is an element named <msn_message> inside
this file, it looks like: 

<msn_message>
<msn_message_type> 
...
...
... 
</msn_message_type>
<prod_rel name="ABC" start_rel="aa" end_rel="bb"/>
<prod_rel name="XYZ" start_rel="cc" end_rel="dd"/>
<other elements.../>
</msn_message> 
This is my requirements: 

1). if ABC = XYZ and either bb or dd greater than 6.0, then 
<msn_message>
<msn_message_type> 
...
...
... 
</msn_message_type>
<prod_rel name="ABC"/>
<other elements.../>
</msn_message> 

2). if ABC != XYZ and both bb and dd are less than 6.0, then
the entire element <msn_message> should be removed. 
My difficulty is:
1). How to compare bb and dd, they are in different element(in the same
level).
2). How to delete the entire element in this case. 

Thanks 

Guo