Enchanted Artifacts and their Uses

I'm looking for clarification as to the different types of weapons and troops my enchanted artifacts are good against. For example I have rings, amulets, weapons and armour that have various bonuses against siege weapons, wheeled units, heavy units, destroyer units, armoured units, machine units which all sound similar. What is the difference between siege and destroyer units for example? I have looked for a definitive list on the forum but can't find one so if anyone can shed some light on what the differences are I would be grateful. 

These are all classes and attributes of units. If you open a unit window you will see a number of symbols at the bottom of the unit window. 

For example, open the window on a chariot unit and under "traits" you will see various symbols. So you artifacts that have powers for Wheeled, Armored, Construct, Mounted,  etc will do extra damage to the Chariot.

You should start to see the destroyer class in later ages.