RFC 4267 INFORMATIONAL SPEECH · MARKUP · WEB
The W3C Speech Interface Framework Media Types: application/voicexml+xml, application/ssml+xml, application/srgs, application/srgs+xml, application/ccxml+xml, and application/pls+xml
Official media types for W3C voice and speech languages
RFC EDITOR
Froumentin, M., "The W3C Speech Interface Framework Media Types: application/voicexml+xml, application/ssml+xml, application/srgs, application/srgs+xml, application/ccxml+xml, and application/pls+xml", RFC 4267, DOI 10.17487/RFC4267, November 2005, <https://www.rfc-editor.org/info/rfc4267>.
BIBTEX
@misc{rfc4267,
series = {Request for Comments},
number = 4267,
howpublished = {RFC 4267},
publisher = {RFC Editor},
doi = {10.17487/RFC4267},
url = {https://www.rfc-editor.org/info/rfc4267},
author = {M. Froumentin},
title = {{The W3C Speech Interface Framework Media Types: application/voicexml+xml, application/ssml+xml, application/srgs, application/srgs+xml, application/ccxml+xml, and application/pls+xml}},
pagetotal = 9,
year = 2005,
month = nov,
} RFC text
Contents
Network Working Group M. Froumentin
Request for Comments: 4267 W3C
Category: Informational November 2005
The W3C Speech Interface Framework Media Types:
application/voicexml+xml, application/ssml+xml, application/srgs,
application/srgs+xml, application/ccxml+xml, and application/pls+xml
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document defines the media types for the languages of the W3C
Speech Interface Framework, as designed by the Voice Browser Working
Group in the following specifications: the Voice Extensible Markup
Language (VoiceXML), the Speech Synthesis Markup Language (SSML), the
Speech Recognition Grammar Specification (SRGS), the Call Control XML
(CCXML), and the Pronunciation Lexicon Specification (PLS).
Table of Contents
1. Introduction ....................................................2
2. Registration of application/voicexml+xml, application/ssml+xml,
application/srgs+xml, application/ccxml+xml, and
application/pls+xml .............................................3
2.1. Encoding Considerations ....................................3
2.2. Interoperability Considerations ............................3
2.3. Published Specifications ...................................3
2.4. Applications that Use These Media Types ....................4
2.5. Security Considerations ....................................4
2.6. Additional Information .....................................4
2.6.1. Magic Numbers .......................................4
2.6.2. File Extensions .....................................4
2.6.3. Fragment Identifiers ................................5
2.6.4. Macintosh File Type Code ............................5
2.6.5. Person and Email Address to Contact for
Further Information .................................5
2.6.6. Intended Usage ......................................5
2.6.7. Change Controller ...................................5
3. Registration of application/srgs ................................5
3.1. Encoding Considerations ....................................5
3.2. Interoperability Considerations ............................5
3.3. Published Specifications ...................................5
3.4. Applications That Use This Media Type ......................6
3.5. Security Considerations ....................................6
3.6. Additional Information .....................................6
3.6.1. Magic Numbers .......................................6
3.6.2. File Extensions .....................................6
3.6.3. Macintosh File Type Code ............................6
3.6.4. Person and Email Address to Contact for
Further Information .................................7
3.6.5. Intended Usage ......................................7
3.6.6. Change Controller ...................................7
4. IANA Considerations .............................................7
5. Normative References ............................................7
1. Introduction
This specification defines the media types of the Voice Extensible
Markup Language (VoiceXML), the Speech Synthesis Markup Language
(SSML), the Speech Recognition Grammar Specification (SRGS), the Call
Control XML (CCXML), and the Pronunciation Lexicon Specification
(PLS), the specifications of the W3C Speech Interface Framework.
VoiceXML ([VoiceXML2.0]) is an Extensible Markup Language (XML)
designed for creating audio dialogs that feature synthesized speech,
digitized audio, recognition of spoken and DTMF key input, recording
of spoken input, telephony, and mixed initiative conversations. The
associated media type defined in this document is
"application/voicexml+xml".
The Speech Synthesis Markup Language specification (SSML) defines an
XML-based markup language for assisting the generation of synthetic
speech in Web and other applications. The essential role of SSML is
to provide authors of synthesizable content a standard way to control
aspects of speech such as pronunciation, volume, pitch, and rate,
across different synthesis-capable platforms. The associated media
type defined in this document is "application/ssml+xml".
The Speech Recognition Grammar Specification (SRGS) defines syntax
for representing grammars for use in speech recognition so that
developers can specify the words and patterns of words to be listened
for by a speech recognizer. The syntax of the grammar format exists
in two forms, an Augmented BNF (ABNF) Form and an XML Form. The
respective media types defined in this document are
"application/srgs" and "application/srgs+xml".
The Call Control EXtensible Markup Language (CCXML) is an XML
designed to provide telephony call control support for dialog
systems, such as VoiceXML. The associated media type defined in this
document is "application/ccxml+xml".
The Pronunciation Lexicon Specification (PLS) defines an XML syntax
for specifying pronunciation lexicons to be used by speech
recognition and speech synthesis engines in voice browser
applications. The associated media type defined in this document is
"application/pls+xml".
2. Registration of application/voicexml+xml, application/ssml+xml,
application/srgs+xml, application/ccxml+xml, and application/pls+xml
MIME media type name: application
MIME subtype names: voicexml+xml, ssml+xml, srgs+xml, ccxml+xml,
pls+xml
Required parameters: none
Optional parameters:
"charset": This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in RFC
3023 [RFC3023].
2.1. Encoding Considerations
Identical to those of "application/xml" as described in RFC 3023
[RFC3023], section 3.2.
2.2. Interoperability Considerations
There are no known interoperability issues.
2.3. Published Specifications
Voice Extensible Markup Language 2.0 [VoiceXML2.0]
Voice Extensible Markup Language 2.1 [VoiceXML2.1]
Speech Synthesis Markup Language (SSML) Version 1.0 [SSML]
Speech Recognition Grammar Specification Version 1.0 [SRGS]
Voice Browser Call Control: CCXML Version 1.0 [CCXML]
Pronunciation Lexicon Specification (PLS) Version 1.0 [PLS]
2.4. Applications that Use These Media Types
Various W3C Speech Interface Framework implementations use these
media types.
2.5. Security Considerations
Several instructions in the cited specifications may cause arbitrary
Uniform Resource Identifiers (URIs) to be dereferenced. In this
case, the security issues of [RFC3986], section 7, should be
considered.
In addition, because of the extensibility features of those
specifications, it is possible that the registered media types may
describe content that has security implications beyond those
described here. However, if the processor follows only the normative
semantics of the specifications, this content will be ignored. Only
in the case where the processor recognizes and processes the
additional content, or where further processing of that content is
dispatched to other processors, would security issues potentially
arise. And in that case, they would fall outside the domain of this
registration document.
2.6. Additional Information
2.6.1. Magic Numbers
Although no byte sequences can be counted on to always be present,
XML MIME entities in ASCII-compatible charsets (including UTF-8)
often begin with hexadecimal 3C 3F 78 6D 6C ("<?xml"), and those in
UTF-16 often begin with hexadecimal FE FF 00 3C 00 3F 00 78 00 6D 00
6C or FF FE 3C 00 3F 00 78 00 6D 00 6C 00 (the Byte Order Mark (BOM)
followed by "<?xml"). For more information, see Appendix F of [XML].
2.6.2. File Extensions
VoiceXML files: .vxml
SSML files: .ssml
SRGS files (XML syntax): .grxml
CCXML files: .ccxml
PLS files: .pls
2.6.3. Fragment Identifiers
Identical to that of "application/xml" as described in RFC 3023
[RFC3023], section 5.
2.6.4. Macintosh File Type Code
"TEXT"
2.6.5. Person and Email Address to Contact for Further Information
World Wide Web Consortium <web-human@w3.org>
2.6.6. Intended Usage
COMMON
2.6.7. Change Controller
The Speech Interface Framework specifications set is a work product
of the World Wide Web Consortium's Voice Browser Working Group. The
W3C has change control over these specifications.
3. Registration of application/srgs
MIME media type name: application
MIME subtype names: srgs
Required parameters: none
Optional parameters: none
3.1. Encoding Considerations
The ABNF Form of SRGS follows the character encoding handling defined
for XML: an ABNF grammar processor must accept both the UTF-8 and
UTF-16 encodings of ISO/IEC 10646 and may support other character
encodings.
3.2. Interoperability Considerations
There are no known interoperability issues.
3.3. Published Specifications
Speech Recognition Grammar Specification Version 1.0 [SRGS]
3.4. Applications That Use This Media Type
Various SRGS implementations use this media type.
3.5. Security Considerations
Several instructions in SRGS may cause arbitrary URIs to be
dereferenced. In this case, the security issues of [RFC3986],
section 7, should be considered.
In addition, because of the extensibility features of SRGS, it is
possible that the registered media types may describe content that
has security implications beyond those described here. However, if
the processor follows only the normative semantics of the
specifications, this content will be ignored. Only in the case where
the processor recognizes and processes the additional content, or
where further processing of that content is dispatched to other
processors, would security issues potentially arise. In that case,
they would fall outside the domain of this registration document.
3.6. Additional Information
3.6.1. Magic Numbers
The ABNF self-identifying header must be present in any legal stand-
alone ABNF Form grammar document. The first character of an ABNF
document must be the "#" symbol (x23) unless preceded by an optional
XML 1.0 byte order mark. The ABNF byte order mark follows the XML
definition and requirements. For example, documents encoded in UTF-
16 must begin with the byte order mark. The optional byte order mark
and required "#" symbol must be followed immediately by the exact
string "ABNF" (x41 x42 x4d x46) or the appropriate equivalent for the
document's encoding (e.g., for UTF-16 little-endian: x23 x00 x41 x00
x42 x00 x4d x00 x46 x00). If the byte order mark is absent on a
grammar encoded in UTF-16, then the grammar processor should perform
auto-detection of character encoding in a manner analogous to auto-
detection of character encoding in XML. Next follows a single-space
character (x20) and the required version number, which is "1.0" for
this specification (x31 x2e x30).
3.6.2. File Extensions
.gram
3.6.3. Macintosh File Type Code
"TEXT"
3.6.4. Person and Email Address to Contact for Further Information
World Wide Web Consortium <web-human@w3.org>
3.6.5. Intended Usage
COMMON
3.6.6. Change Controller
The SRGS specification is a work product of the World Wide Web
Consortium's Voice Browser Working Group. The W3C has change control
over the SRGS specification.
4. IANA Considerations
This document registers six new MIME media types, according to the
registrations in Section 2 and Section 3.
5. Normative References
[CCXML] Auburn, RJ., Ed., "Voice Browser Call Control: CCXML
Version 1.0, W3C Working Draft", January 2005,
<http://www.w3.org/TR/2005/WD-ccxml-20050111/>.
[PLS] Baggia, P., Ed., "Pronunciation Lexicon Specification
(PLS) Version 1.0, W3C Working Draft", February 2005,
<http://w3.org/TR/2005/WD-pronunciation-lexicon-
20050214/>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[SRGS] Hunt, A., Ed. and S. McGlashan, Ed., "Speech
Recognition Grammar Specification Version 1.0, W3C
Recommendation", March 2004,
<http://www.w3.org/TR/2004/REC-speech-grammar-
20040316/>.
[SSML] Burnett, D., Ed., Walker, M., Ed., and A. Hunt, Ed.,
"Speech Synthesis Markup Language (SSML) Version 1.0,
W3C Recommendation", September 2004,
<http://www.w3.org/TR/2004/REC-speech-synthesis-
20040907/>.
[VoiceXML2.0] McGlashan, S., Ed., "Voice Extensible Markup Language
(VoiceXML) Version 2.0, W3C Recommendation", March
2004, <http://www.w3.org/TR/2004/REC-voicexml20-
20040316/>.
[VoiceXML2.1] Oshry, M., Ed., "Voice Extensible Markup Language
(VoiceXML) Version 2.1, W3C Working Draft", July 2004,
<http://www.w3.org/TR/2004/WD-voicexml21-20040728/>.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E.,
and F. Yergeau, "Extensible Markup Language (XML) 1.0
(Third Edition)", February 2004,
<http://www.w3.org/TR/2004/REC-xml-20040204/>.
Author's Address
Max Froumentin
World Wide Web Consortium
EMail: mf@w3.org
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AI ELI5
On this page
PROBLEMVoice application builders need standard ways to identify and process five W3C Speech Interface Framework languages (VoiceXML, SSML, SRGS, CCXML, and PLS).
MECHANISMRFC 4267 registers six MIME media types for these languages, with both XML (+xml) and ABNF variants, allowing software to recognize files by their content type.
WHY IT MATTERSApplications can now handle voice interface files correctly and interoperably by looking up the registered media types.
§1Voice Interface Framework Overview
The W3C Speech Interface Framework is a collection of five specifications designed for building voice-based applications. VoiceXML is an XML language for creating audio dialogs with synthesized speech, voice recognition, and DTMF key input. SSML (Speech Synthesis Markup Language) lets developers control speech synthesis details like pronunciation, volume, pitch, and rate. SRGS (Speech Recognition Grammar Specification) defines the words and patterns a speech recognizer should listen for, with both ABNF and XML syntax forms. CCXML (Call Control XML) provides telephony call control for dialog systems. PLS (Pronunciation Lexicon Specification) specifies pronunciation for speech engines.
These are five different languages for building voice apps. Each one does a different job, like playing voice messages or understanding what someone said.
§2MIME Type Registration
RFC 4267 registers six MIME media types. Five languages get XML-based types: application/voicexml+xml, application/ssml+xml, application/srgs+xml, application/ccxml+xml, and application/pls+xml. The SRGS grammar format also has a non-XML ABNF form registered as application/srgs. All types are in the application category. The only optional parameter across all types is charset, which follows the same rules as application/xml.
The RFC says 'When you get a file with this label, it is a VoiceXML file' (or SSML, or one of the others). Now programs know what they are receiving.
§3Format Details and File Extensions
The XML-based media types inherit encoding and fragment identifier rules from RFC 3023. VoiceXML files use the .vxml extension, SSML uses .ssml, SRGS XML grammar uses .grxml, CCXML uses .ccxml, and PLS uses .pls. The ABNF form of SRGS uses the .gram extension and requires a self-identifying header: the file must start with a '#' symbol followed by 'ABNF' and a version number (like '1.0' for this specification). Both XML and ABNF forms must support UTF-8 and UTF-16 encodings.
Each type has a file extension so humans and programs can see what kind of file it is at a glance, like '.vxml' for voice files.
§4Security Implications
Since these languages can reference external URIs, the security considerations from RFC 3986 apply. For example, a VoiceXML file might tell a phone to fetch a voice prompt from a URL, which requires careful validation. All five specifications have extensibility features that might carry unexpected content. However, RFC 4267 notes that if a processor strictly follows only the normative semantics specified in the W3C documents, any extension content will be ignored. Security issues only arise if the processor chooses to recognize and process non-normative extensions, which then falls outside this registration document's scope.
Files can point to other files on the internet, so be careful about where the files come from, like checking that a URL is trustworthy before using it.
§5Interoperability and Applications
There are no known interoperability issues with these media type registrations. Various W3C Speech Interface Framework implementations use these media types to exchange voice interface files across systems. The W3C Voice Browser Working Group maintains control over the specifications themselves. Organizations implementing voice systems can register these media types with their web servers and content management systems, ensuring that voice interface files are served with the correct MIME type headers. This enables client applications to automatically recognize and process voice files correctly.
Many companies have built tools that understand these languages. Once they know the file type from the MIME label, they can handle it correctly.