Base Damage is a special Attribute which, unlike Melee Damage, cannot be directly seen by the Player during gameplay.
The Base Damage depends on the Creature or the Player, and respectively, the Weapon used. Same Creatures and Weapons also have the same Base Damage.
Disregarding Armor, resulting damage is calculated by multiplying the Base Damage, an absolute number, by the percentage coming from the Melee Damage Attribute.
The difference between Base Damage and Melee Damage is that only the latter can be seen ingame. This may lead to confusion of the player because it does not seem obvious that Melee Damage is not the only Attribute affecting the damage.
Higher Melee Damage does not necessarily mean higher resulting damage.