These are one of the oldest and most popular generators. This approach allows designers to creatively achieve content by generating a game map. The designers can specify an underlying set of components with each component being able to produce a specific type of content. The components are united through the n-ary tree structure, providing a tree view that can be customized to match the designer's workflow.
For example, in a RPG with an onset of levels of difficulty as well as a branching story line, a tree would handle all these things. The first branching is when you choose to start the game (here the path branches into difficulty levels). The next branching (plot) happens when the player makes a choice about how he wants to proceed. To handle all possible outcomes, the tree is built from the root downwards. Each result that is reached flows onto the next branches of the tree.
Many systems have been presented at this conference, here is a video summary of what you could use to develop your game with Houdini. A playlist of the conference presentations is also available at https://www.youtube.com/watch?v=lgXSokxK8pM .
For example by using Chaining Vectors. The chaining file assigns a component to a vertex. If the component tree is directed, then the vertex will be linked to the component itself, but if it is undirected the vertex will be linked to its parent. d2c66b5586