The PlayStation 4 launch title Killzone Shadow Fall will be switching to challenges instead of XP for multiplayer progression. Guerrilla Games explained more about the switch, including the types of challenges and how it impacts the use of bots.
A post on the game's official site says that the game will have more than 1500 challenges in all. Those can range from the more general like destroying one turret, to the extremely specific: "Kill 1 enemy player with Laser Tripmine while they are carrying a Beacon." Each challenge adds a point to your rank, and also rewards you with weapon attachments, new abilities, and character visual modifiers.
As a result, this also touches on the issue of bots. You can run a match with bots filling in for empty slots, automatically swapping for dropped players, or even have a team of humans against bots. In offline mode, though, you won't be able to complete challenges using bots. You'll need to earn those ranks fair and square.