Grammar Headers
ABNF and XML grammar files must contain specific header
information; otherwise, the VoiceXML interpreter will fail to
recognize the grammar properly. The elements of a grammar file are:
- grammar declaration
- language/locale
- mode
- root grammar
ABNF
# ABNF 1.0 ISO-8859-1;
language en;
mode voice;
root $topRule;
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<grammar version="1.0"
xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en" mode="voice" root="topRule">
...
Grammar declaration
The grammar declaration specifies the grammar version and
optionally, the character encoding scheme that should be used. The
grammar version should always be set to 1.0. The character
encoding specifies the character symbols that will be used for the
grammar. For example, ISO-8859-1 is usually the character encoding
used for English. Asian languages including Japanese and Chinese
(Big5 or Mandarine) would use a different encoding scheme. In ABNF
grammars, this is the first line. In XML, the encoding scheme is
defined by the encoding attribute of the XML declaration (the
first line of any XML file).
ABNF
# ABNF 1.0 ISO-8859-1;
language en;
mode voice;
root $topRule;
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<grammar version="1.0"
xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en" mode="voice" root="topRule">
...
The grammar version in an XML grammar is defined by the version
attribute of the <grammar> element.
Language
Unless the grammar is a DTMF grammar, a language must be
specified in the grammar header. For ABNF grammars, the language
parameter defines the language (in this example, US English):
ABNF
# ABNF 1.0 ISO-8859-1;
language en;
mode voice;
root $topRule;
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<grammar version="1.0"
xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en" mode="voice" root="topRule">
...
The language in an XML grammar is specified by the xml:lang attribute of the <grammar> element.
Mode
Grammars can be scoped for speech input (voice) or
touch-tone input (dtmf) based on the value of the mode
parameter. The default mode is voice. If the grammar is
scoped dtmf, then speech input will not be recognized.
VoiceXML 2.0 grammars do not allow mixed mode grammars. That means
that a voice scoped grammar cannot include a dtmf
scoped grammar or vice versa. In cases where we may want an
application to accept both voice and DTMF input, two separate
grammars can be defined within a given VoiceXML scope so long as
they aren't combined into a single grammar in any way.
ABNF
# ABNF 1.0 ISO-8859-1;
language en;
mode voice;
root $topRule;
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<grammar version="1.0"
xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en" mode="dtmf" root="topRule">
...
Root grammar
When grammars contain many sub-grammar rules in a single file,
it's important to identify the root grammar, or main the grammar
that will be executed when a VoiceXML dialog calls the grammar
file.
ABNF
# ABNF 1.0 ISO-8859-1;
language en;
mode voice;
root $topRule;
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<grammar version="1.0"
xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en" mode="voice" root="topRule">
...
Filename Extensions
The filename extension for ABNF grammars is .gram
and .grxml for XML grammars. This is the recommended (but not
required) filename extension format for grammar files.
About Jonathan Eisenzopf
Jonathan is a member of The Ferrum Group, LLC which specializes in Voice Web consulting and training. Feel free to send an email to eisen@ferrumgroup.com regarding questions or comments about this or any article.
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