One of the difficulties of Wizard of Oz prototyping is that each scenario needs to be carefully designed, and how the wizard will respond carefully orchestrated. The time spent doing this prevents using Wizard of Oz prototyping iteratively. Each iteration is just too expensive.
The reading is about a system that attempts to reduce these costs. Georgia Institute of Technology developed a system, DART, that provides a set of tools for testing augmented reality applications. It’s a publish/subscription system that relies on reacting to events. For Wizard of Oz prototyping, the system can publish events such as user proximity or situation, forward it to the wizard, who can respond appropriately. Responses are tied to specific events, reducing the time needed to search for an appropriate response to an event.
The reading has a case study that uses the DART system to guide users on a tour of the Oakland cemetery in Atlanta. As users visit certain locations, information is provided to the user about what they are seeing. If they want more information the system lets them delve deeper. Of course, the actual system isn’t built for these tests. Instead, the ‘computer’ responses are given by the wizard. For the first test, the wizard controlled the entire system. For the second and third tests, the wizard controlled fewer and fewer elements of the system.