麻烦使用Nokogiri解析XML文件

I have a code written to parse an XML file in ruby using 'nokogiri' gem. However the logic that i have currently goes and fetches an entire nodeset but what i really want i to do is go fetch the value of an particular attribute in the nodeset. Need some help on how to achieve this using nokogiri???I have a code written to parse an XML file in r