Q: Whatabout links? How do they really come into play in VoiceXML programming?
A: Once you understand how forms, fields, and grammars interact, the notion of "links" in VoiceXML is a very straightforward thing to add. As you might imagine, a very common thing developers want to do in VoiceXML applications is add some measure of "universal commands" that are always available, and always behave in the same way.
It would certainly be possible- though by no means practical- to write the grammar for these commands, save it to a separate file, reference it in every form in every document in your application, and then write the proper logic in every field of every form of every document to react in the right way if the caller actually says one of these things. With this in mind, VoiceXML has support for the notion of "links".
VoiceXML links (defined by the element) are very simple- they define a grammar and either an event to throw or a URL to transition to; if the caller ever says something to match the link's grammar, control is whisked away from the current field and the specified transition or event is executed. Links can be specified at any scope (from an application root document down through within an individual field), and their grammars are only active within the scope where the link is specified.
Links that fire events are a particularly good way to handle universal commands, because the flexible and hierarchical event model (see later in this chapter for detail, but you're probably already getting the picture) make it easy to specify global event handlers at the application level, and override them locally when and if needed.
In our simple example of using links within a single document application; the general concept extends easily to more complex applications. That's really all there is to it. Using links (and associated event handlers) throughout applications is a flexible technique commonly used by professional VoiceXML developers.
