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VoiceXML
in the Large
(Continued
from Part 1)
Abstraction
of Components
Abstraction of application components is an important
software development technique. In the case of VoiceXML,
much of the abstraction can be delegated to the server-side
implementation.
Once
you start developing VoiceXML applications however,
you will soon find that there are certain dialogs that
you are going to need over and over again. For example,
the confirmation of input, or the collection of a specific
piece of information such as a phone number. Vendors
in the speech industry have invested a great deal of
effort in designing the 'call flow', grammars, and prompts
for these dialogs, so that they are very good at accurately
gathering the information in which you're interested.
Wouldn't it be great to be able reuse that experience?
Well, with the VoiceXML <subdialog> tag, you can.
Subdialogs
allow you to encapsulate a reusable dialog, and reuse
it in many applications. A subdialog provides the following
features:
- A
subdialog can be 'built-in', defined in the VoiceXML
page, or referenced as a server-side component;
- A
subdialog is parameterized (using the <param>
tag), allowing the tailoring of the subdialog in very
powerful ways;
- Invocation
of a subdialog can include handling of events in the
same manner as a field (and in fact is used like a
field in a form);
- A
subdialog returns a set of variables to the calling
document (using the <return> tag).
Samples
of useful subdialogs include:
- Credit
card number collection;
- Confirmation
of a previous input;
- Collection
of a date (including support for different inputs,
like "yesterday", "next Monday",
or "July 25, 2001");
Subdialogs
can be used to build much larger user interactions,
while avoiding common mistakes and taking advantage
of hard-won experience.
Application
Partitioning
One
of the most common questions asked by new users is "how
do I partition my application between the client and
server?" Our answer to this is usually "pick
the right tool for the right job." You have the
following tools available to you:
- VoiceXML,
controlling real-time speech, DTMF, audio, and TTS
interaction with the user;
- ECMAScript
(part of the VoiceXML specification), providing a
general 'workhorse' component for doing little jobs
that don't require a trip to the server; and
- The
application server component; which provides integration
with database and legacy systems, and links to data
required by the application.
VoiceXML
is best used to control the collection of information
from the caller, validation of that information if possible,
and playback of information to the user.
ECMAscript
is best used to support the VoiceXML part, whether it
is by massaging data formats, doing simple calculations
or whatever. It gives the application author a mechanism
to avoid a round-trip to the server for simple processing
requirements. It also melds nicely with the variable
and object model of the interpreter itself, so that,
for example, field variables and ECMAscript variables
are interchangeable.
The
application server component provides your VoiceXML
application with access to personalized or dynamic information.
By filling a VoiceXML page with information that is
relevant to the caller, or based on current events and
information, you can build a more compelling application.
This is exactly the model that has migrated the web
from being a 'read-only' experience to a much more personalized,
and useful medium.
You
can think of this partitioning in the same way as typical
n-tier web application architectures. Many of the same
issues are relevant, with the exception that the interaction
with the speech user has more stringent response requirements
than the typical web application.
So
the short answer to the question on how to partition
an application is 'it depends', but if you follow the
guidelines above, you'll be off to a good start.
What's
Next?
Next
month, we're going to get back into the more interesting
stuff: coding! We'll show you more about how to build
typical VoiceXML applications, using the concepts we've
learned so far. In the meantime, if you haven't already,
you might want to have a look at these resources provided
by the VoiceXML Forum:
A
number of VoiceXML Forum Members provide access to developer
sites and tool kits that will allow you to try out VoiceXML
for yourself. A few of these are:
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Copyright
© 2001 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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