jurafsky&martin_3rdEd_17 (1).pdf

More sophisticated statistical generation strategies

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More sophisticated statistical generation strategies will be discussed in Sec- tion 29.5 of Chapter 30. 28.3 VoiceXML There are a wide variety of commercial systems that allow developers to implement frame-based dialog systems, such as the user-definable skills in Amazon Alexa or the actions in Google Assistant. Such industrial systems provide libraries for defining the rules for detecting a particular user intent and filling in slots, and for expressing the architecture for controlling which frames and actions the system should take at which times. Instead of focusing on one of these commercial engines, we introduce here a sim- ple declarative formalism that has similar capabilities to each of them: VoiceXML , VoiceXML the Voice Extensible Markup Language ( ), an XML-
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28.3 V OICE XML 435 based dialog design language used to create simple frame-based dialogs. Although VoiceXML is simpler than a full commercial frame-based system (it’s deterministic, and hence only allows non-probabilistic grammar-based language models and rule- based semantic parsers), it’s still a handy way to get a hands-on grasp of frame-based dialog system design. A VoiceXML document contains a set of dialogs, each a menu or a form . A form is a frame, whose slots are called fields . The VoiceXML document in Fig. 28.12 shows three fields for specifying a flight’s origin, destination, and date. Each field has a variable name (e.g., origin ) that stores the user response, a prompt , (e.g., prompt Which city do you want to leave from ), and a grammar that is passed to the speech recognition engine to specify what is allowed to be recognized. The grammar for the first field in Fig. 28.12 allows the three phrases san francisco , barcelona , and new york . The VoiceXML interpreter walks through a form in document order, repeatedly selecting each item in the form, and each field in order. <noinput> I’m sorry, I didn’t hear you. <reprompt/> </noinput> <nomatch> I’m sorry, I didn’t understand that. <reprompt/> </nomatch> <form> <block> Welcome to the air travel consultant. </block> <field name="origin"> <prompt> Which city do you want to leave from? </prompt> <grammar type="application/x=nuance-gsl"> [(san francisco) barcelona (new york)] </grammar> <filled> <prompt> OK, from <value expr="origin"/> </prompt> </filled> </field> <field name="destination"> <prompt> And which city do you want to go to? </prompt> <grammar type="application/x=nuance-gsl"> [(san francisco) barcelona (new york)] </grammar> <filled> <prompt> OK, to <value expr="destination"/> </prompt> </filled> </field> <field name="departdate" type="date"> <prompt> And what date do you want to leave? </prompt> <filled> <prompt> OK, on <value expr="departdate"/> </prompt> </filled> </field> <block> <prompt> OK, I have you are departing from <value expr="origin"/> to <value expr="destination"/> on <value expr="departdate"/> </prompt> send the info to book a flight...
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