# Get overall feel of the xml's structure
xml_elcount file.xml

# Enumerate name attribute values of class node
xml sel -t -v '//class/@name' file.xml | sort > /tmp/lista

# Show common values between two sorted lists
comm -12 /tmp/lista /tmp/listb

# Show values only in lista
comm -23 /tmp/lista /tmp/listb

# Show values only in listb
comm -13 /tmp/lista /tmp/listb