xpath problem

hi ever one

from the fllowing xml fragment
<AA>
<BB>
<category cat_id="1">one</category>
<category cat_id="2">one</category>
<category cat_id="3">two</category>
<category cat_id="4">three</category>
<BB>
<CC>
<sb-category  id="1"  category="1">one</category>
<sb-category  id="2"  category="1">one</category>
<sb-category  id="3"  category="1">two</category>
<sb-category  id="4"  category="3">three</category>
<CC>
<AA>


i am trying to output all sub-category  within <CC> corspondes to a
particuler category within <BB>

my last attempet to achive the desired result was the following but is wrong

can any one please help

thanks


//child::sb-category[attribute::id="1" and
attribute::category=[ancestor::BB/child::category[attribute::cat_id="1"]]]");