Description
From Random Scattering: Creating Realistic Landscapes:
Two competing methodologies in procedural content generation are teleological and ontogenetic. The teleological approach creates an accurate physical model of the environment and the process that creates the thing generated, and then simply runs the simulation, and the results should emerge as they do in nature.
The ontogenetic approach observes the end results of this process and then attempts to directly reproduce those results by ad hoc algorithms. Ontogenetic approaches are more commonly used in real-time applications such as games. (See "Shattering Reality," Game Developer, August 2006.)
A similar (overlapping) distinction is "top down" versus "bottom up": top-down algorithms directly modify/create things to obtain the desired result, and bottom up algorithms create a result that may only have what you want as a side effect (I personally prefer that terminology, it's easier to remember which is which. But they may not refer to exactly the same thing).
This distinction is visible in map generation when you compare your generated map to your desired topology - whether all points can be reached, whether certain specific points (enter? exit? starting point? goal?) are connected to each other, whether there are choke points, etc.
If you're generating a map using Perlin Noise for height, which in turns determines which areas can be crossed (not those above / below a certain height, or with a certain slope), you can't guarantee anything about topology.
But many dungeon and maze generation algorithms directly place rooms and corridors so that they're connected (though some may screw up along the process).
There's a general tradeoff between having good-looking and interesting maps, versus preserving your topological constraints - or more generally, generating something challenging but not completely impossible. You can also loosen up the importance of topological constraints, for example with destructible environments (digging, bombs), or allowing the player to re-generate levels until he finds one he likes.
Teleological Algorithms
Ontogenetic Algorithms
PCG Wiki References
External Links
Random Scattering: Creating Realistic Landscapes - Mick West
