Life in the Shadows
(Continued from
part 1
Transfer
The
<transfer> tag also provides a number a number
of useful shadow variables. Note that all of these
only apply to the 'bridged' case, where
the bridge attribute is 'true'.
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Shadow Variable
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Contents
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Typical Uses
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name$.duration
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Length of the transferred call, in milliseconds.
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Billing, statistics, etc.
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name$.inputmode
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If the call was terminated by either speech or DTMF
input (by the original caller), the mode ('speech' or 'dtmf')
that caused the outbound call to terminate.
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Determining how the call was terminated.
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name$.utterance
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If the call was terminated by speech, then the user
utterance that triggered the recognized grammar.
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Selecting follow-on action (note that grammar within transfer
is optional and not widely supported).
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Last Results
In addition to
those shadow variables associated with each input item, we also
have a general shadow variable for all input collections:
application$.lastresult. This isn't the same kind of
shadow variable as the others, as it doesn't 'shadow' another
particular variable, but rather all input items. The contents
always reflect the results of the last input collection (the
astute among you will see the reason for the name). Note that
'application' isn’t your application name, but the literal word
'application'.
The shadow
variable application$.lastresult is an array of objects,
application$.lastresult[n] with members
application$.lastresult[n].confidence,
application$.lastresult[n].utterance,
application$.lastresult[n].inputmode, and
application$.lastresult[n].interpretation. The array includes
the N-best results (numbered from 0 to a maximum size of maxnbest-1).
You should check the length of the array using the
application$.lastresult.length member before performing any
operations based on application$lastresult. Note also that you
can application$.lastresult.confidence, etc., correspond to the
0th element of the application$.lastresult array.
Another interesting
point regarding application$.lastresult is the fact that it is set
even in the event of a nomatch (this is a recent change to the
specification though). This is really interesting, as it allows you
to try to decide what went wrong in the user interaction, and to make
decisions based upon this. Note that a 'noinput' does not change the
values in application$.lasresult. When the VoiceXML interpreter
is next collecting input, application$.lastresult will be set to
ECMAScript 'undefined'.
Summary
Shadow variables
provide 'under-the-hood' information that can be important tools as
you develop your VoiceXML application. Know what's available and
how to use it, and you’ll be able to develop better applications.
If you get stuck,
make sure that you have a look at whatever platform specific
information is available; there is a tradeoff here, as you sacrifice
portability for features, so consider use of such platform specific
variables carefully.
For some examples
of shadow variables in action, have a look at these previous First
Words columns:
What’s Next?
If there are
particular things you’d like to see covered in a future First
Words column, drop me a line at
rob@voicegenie.com, and I’ll try to write about it.
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© 2001-2002 VoiceXML Forum. All rights reserved.
The VoiceXML Forum is a program of the
IEEE
Industry Standards and Technology Organization (IEEE-ISTO).
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