1.7. Nested conversations: extending the Hotel Booking example

Long-running conversations let you easily maintain state consistency in an application, even in the face of multi-window operation and back-buttoning. Unfortunately, simply beginning and ending a long-running conversation is not always enough. Depending on the requirements of the application, inconsistencies between user expectations and application state can still result.

The nested booking application extends the features of the hotel booking application to incorporate room selection. Each hotel has a list of available rooms from which the user can select. This requires the addition of a room selection page in the hotel reservation flow.

The user can now select any available room to be included in the booking. If room selection were left in the same conversation context, this could lead to issues with state consistency — if a conversation variable changes, it affects all windows operating within the same conversation context.

For example, suppose the user clones the room selection screen in a new window. The user then selects the Wonderful Room and proceeds to the confirmation screen. To check the cost of a more expensive room, the user returns to the original window, selects the Fantastic Suite for booking, and again proceeds to confirmation. After reviewing the total cost, the user returns to the window showing Wonderful Room to confirm.

In this scenario, if all state were stored in the conversation, flexibility for multi-window operation within the same conversation would be limited. Nested conversations allow us to achieve correct behavior even when context can vary within the same conversation.