jurafsky&martin_3rdEd_17 (1).pdf

The speaker in control of any conversation is said to

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the next question. The speaker in control of any conversation is said to have the initiative in the initiative conversation. Systems that completely control the conversation in this way are thus called system-initiative . By contrast, in normal human-human dialog, initiative system- initiative shifts back and forth between the participants ( Bobrow et al. 1977 , Walker and Whit- taker 1990 ).
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28.2 F RAME B ASED D IALOG A GENTS 429 The single-initiative finite-state dialog architecture has the advantage that the system always knows what question the user is answering. This means the system can prepare the speech recognizer with a language model tuned to answers for this question, and also makes natural language understanding easier. Most finite-state systems also allow universal commands that can be said anywhere in the dialog, universal like help , to give a help message, and start over (or main menu ), which returns the user to some specified main start state,. Nonetheless such a simplistic finite-state architecture is generally applied only to simple tasks such as entering a credit card number, or a name and password. For most applications, users need a bit more flexibility. In a travel-planning situation, for example, a user may say a sentence that fills multiple slots at once: (28.3) I want a flight from San Francisco to Denver one way leaving after five p.m. on Tuesday. Or in cases where there are multiple frames, a user may say something to shift frames, for example from airline reservations to reserving a rental car: (28.4) I’d like to book a rental car when I arrive at the airport. The standard GUS architecture for frame-based dialog systems, used in various forms in modern systems like Apple’s Siri, Amazon’s Alexa, and the Google Assis- tant, therefore follows the frame in a more flexible way. The system asks questions of the user, filling any slot that the user specifies, even if a user’s response fills mul- tiple slots or doesn’t answer the question asked. The system simply skips questions associated with slots that are already filled. Slots may thus be filled out of sequence. The GUS architecture is thus a kind of mixed initiative , since the user can take at mixed initiative least a bit of conversational initiative in choosing what to talk about. The GUS architecture also has condition-action rules attached to slots. For ex- ample, a rule attached to the DESTINATION slot for the plane booking frame, once the user has specified the destination, might automatically enter that city as the de- fault StayLocation for the related hotel booking frame. Once the system has enough information it performs the necessary action (like querying a database of flights) and returns the result to the user. We mentioned in passing the linked airplane and travel frames. Many domains, of which travel is one, require the ability to deal with multiple frames. Besides frames for car or hotel reservations, we might need frames with general route in- formation (for questions like Which airlines fly from Boston to San Francisco? ),
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