chef is additive by nature. Removing resource definitions from recipes will not remove the resources from the system. This can be confusing for beginner chefs. An authoritative resource set is a term used to describe a resource set containing only the resources defined in the chef recipes.
The "zap" pattern emerged as a way to build authoritative resource sets. The LWRPs from the zap cookbook, https://github.com/nvwls/zap, will be presented as well as various use cases.
This talk was presented at ChefConf 2014.