Slot filling models are a useful method for simple natural language understanding tasks, where information can be extracted from a sentence and used to perform some structured action As candidate tasks, we consider the actions that a user might perform via apps on their phone. Crowd-sourced data was collected simulating common use cases for four different apps: United Airlines, Airbnb, Greyhound bus service and OpenTable. The corresponding actions are booking a flight, renting a home, buying bus tickets, and making a reservation at a restaurant. 
 Question: What tasks are they experimenting with in this paper?
Slot filling we consider the actions that a user might perform via apps on their phone The corresponding actions are booking a flight, renting a home, buying bus tickets, and making a reservation at a restaurant