It was my understanding that hop chemistry is split into 2 distinct parts, bittering and flavoring/aroma.
Bittering is described by Alpha and Beta acids, the most important being the percentage that is made up Cohumulone. Higher Cohumulone supposedly has "harsher" bittering. (I don't think "harsher" is meant as a negative description, ie - Columbus @ 33% Cohumulone vs. Simcoe @ 17% Cohumulone)
Flavoring/aroma is comprised of the essential oils, mainly Myrcene, Humulene, Caryophylene and Farnesene. Their percentage listed is their portion of the essential oils in the hops and should add up to less than 100% because there are a whole bunch of other lesser known essential oils in hops also.
The example of Ahtanum:
Cohumulone 30-35% is the percentage of Alpha Acids comprised of Cohumulone. It affects bittering
Myrcene 50-55% is the percentage of essential oils comprised of Myrcene. It affects flavor/aroma
Myrcene+Humulene+Caryophyllene+Farnesene = 75%, so 25% are other lesser known essential oils.
Rules of thumb -
total Alpha Acid percentage indicates potential bittering power.
Cohumulone percentage indicates the type of bittering flavor.
Total essential oils indicates the potential flavoring/aroma power.
Ratios of each of Myrcene, Humulene, Caryophyllene, Farnesene to the total essential oils determines the flavor/aroma profile.
check these references for some more insight:
My understanding of HOPS need-help!
HBT Wiki - Hop Chemistry