Speech Recognition Grammar Specification

Speech Recognition Grammar Specification (SRGS) is a W3C standard for how "speech recognition grammars" are specified. A speech recognition grammar is a set of word patterns, and tells a speech recognition system what to expect a human to say. For instance, if you call a voice directory application, it will prompt you for the name of the person you would like to talk with. It will then start up a speech recognizer, giving it a speech recognition grammar. This grammar contains the names of the people in the directory, and the various sentence patterns callers typically respond with.

SRGS specifies two alternate but logically equivalent syntaxes, one based on XML, and one using Augmented BNF format. In practice, the XML syntax is used more frequently.

If the speech recognizer returned just a string containing the actual words spoken by the user, the voice application would have to do the tedious job of extracting the semantic meaning from those words. For this reason, SRGS grammars can be decorated with "tag" elements, which when executed, build up the semantic result. SRGS does not specify the contents of the tag elements: this is done in a companion W3C standard, Semantic Interpretation for Speech Recognition (SISR). SISR is based on ECMAScript, and ECMAScript statements inside the SRGS tags build up an ECMAScript semantic result object that is easy for the voice application to process.

Both SRGS and SISR are W3C Recommendations, the final stage of the W3C standards track. The W3C VoiceXML standard, which defines how voice dialogs are specified, depends heavily on SRGS and SISR.

Examples

Here is an example of the Augmented BNF form of SRGS, as it could be used in a voice directory application:

#ABNF 1.0 ISO-8859-1; // Default grammar language is US English language en-US; // Single language attachment to tokens // Note that "fr-CA" (Canadian French) is applied to only // the word "oui" because of precedence rules $yes = yes | oui!fr-CA; // Single language attachment to an expansion $people1 = (Michel Tremblay | André Roy)!fr-CA; // Handling language-specific pronunciations of the same word // A capable speech recognizer will listen for Mexican Spanish and // US English pronunciations. $people2 = Jose!en-US; | Jose!es-MX; /** * Multi-lingual input possible * @example may I speak to André Roy * @example may I speak to Jose */ public $request = may I speak to ($people1 | $people2);

Here is the same SRGS example, using the XML form:

yes oui Michel Tremblay André Roy Jose Jose may I speak with André Roy may I speak with Jose may I speak with

ee also

* SISR
* VoiceXML
* Pronunciation Lexicon Specification (PLS)
* Natural Language Semantics Markup Language

External links

* [http://www.w3.org/TR/speech-grammar/ SRGS Specification (W3C Recommendation)]
* [http://www.w3.org/TR/semantic-interpretation/ SISR Specification (W3C Recommendation)]
* [http://www.voicexml.org VoiceXML Forum]