Pronunciation Lexicon Specification

The Pronunciation Lexicon Specification (PLS) is a W3C Recommendation, which is designed to enable interoperable specification of pronunciation information for both speech recognition and speech synthesis engines within voice browsing applications. The language is intended to be easy to use by developers while supporting the accurate specification of pronunciation information for international use.

The language allows one or more pronunciations for a word or phrase to be specified using a standard pronunciation alphabet or if necessary using vendor specific alphabets. Pronunciations are grouped together into a PLS document which may be referenced from other markup languages, such as the Speech Recognition Grammar Specification SRGS and the Speech Synthesis Markup Language SSML.

Usage

Here is an example PLS document:

 <?xml version="1.0" encoding="UTF-8"?>
 <lexicon version="1.0" 
     xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 
       http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"
     alphabet="ipa" xml:lang="en-US">
   <lexeme>
     <grapheme>judgment</grapheme>
     <grapheme>judgement</grapheme>
     <phoneme>ˈdʒʌdʒ.mənt</phoneme>
     <!-- IPA string is:
       "&#x02C8;d&#x0292;&#x028C;d&#x0292;&#x002E;m&#x0259;nt" --> 
   </lexeme>
   <lexeme>
     <grapheme>fiancé</grapheme>
     <grapheme>fiance</grapheme>
     <phoneme>fiˈɒns.eɪ</phoneme>
     <!-- IPA string is:
       "fi&#x02C8;&#x0252;ns&#x002E;e&#x026A;" --> 
     <phoneme>ˌfiː.ɑːnˈseɪ</phoneme>
     <!-- IPA string is:
       "&#x02CC;fi&#x02D0;&#x002E;&#x0251;&#x02D0;n&#x02C8;se&#x026A;" --> 
   </lexeme>
 </lexicon>

which could be used to improve TTS as shown in the following SSML 1.0 document:

 <?xml version="1.0" encoding="UTF-8"?>
 <speak version="1.0" 
     xmlns="http://www.w3.org/2001/10/synthesis" 
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
       http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
     xml:lang="en-US">
   <lexicon uri="http://www.example.org/lexicon_defined_above.xml"/>
   <p> In the judgement of my fiancé, Las Vegas is the best place for a honeymoon.
       I replied that I preferred Venice and didn't think the Venetian casino was an
       acceptable compromise.</p>
 </speak>

but also to improve ASR in the following SRGS 1.0 grammar:

 <?xml version="1.0" encoding="UTF-8"?>
 <grammar version="1.0"
     xmlns="http://www.w3.org/2001/06/grammar"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xsi:schemaLocation="http://www.w3.org/2001/06/grammar 
       http://www.w3.org/TR/speech-grammar/grammar.xsd"
     xml:lang="en-US" root="movies" mode="voice">
   <lexicon uri="http://www.example.org/lexicon_defined_above.xml"/>
   <rule id="movies" scope="public">
     <one-of>
             <item>Terminator 2: Judgment Day</item> 
             <item>My Big Fat Obnoxious Fiance</item> 
             <item>Pluto's Judgement Day</item>
     </one-of> 
   </rule>
 </grammar>

Common Use Cases

Multiple pronunciations for the same orthography

For ASR systems it is common to rely on multiple pronunciations of the same word or phrase in order to cope with variations of pronunciation within a language. In the Pronunciation Lexicon language, multiple pronunciations are represented by more than one <phoneme> (or <alias>) element within the same <lexeme> element.

In the following example the word "Newton" has two possible pronunciations.

 <?xml version="1.0" encoding="UTF-8"?>
 <lexicon version="1.0" 
      xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 
        http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"
      alphabet="ipa" xml:lang="en-GB">
   <lexeme>
     <grapheme>Newton</grapheme>
     <phoneme>ˈnjuːtən</phoneme>
     <!-- IPA string is: "&#x02C8;nju&#x02D0;t&#x0259;n" -->
     <phoneme>ˈnuːtən</phoneme>
     <!-- IPA string is: "&#x02C8;nu&#x02D0;t&#x0259;n" -->
   </lexeme>
 </lexicon>

Multiple orthographies

In some situations there are alternative textual representations for the same word or phrase. This can arise due to a number of reasons. See Section 4.5 of PLS for details. Because these are representations that have the same meaning (as opposed to homophones), it is recommended that they be represented using a single <lexeme> element that contains multiple graphemes.

Here are two simple examples of multiple orthographies: alternative spelling of an English word and multiple writings of a Japanese word.

 <?xml version="1.0" encoding="UTF-8"?>
 <lexicon version="1.0" 
      xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 
        http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"
      alphabet="ipa" xml:lang="en-US">
   <!-- English entry showing how alternative spellings are handled -->
   <lexeme>
     <grapheme>colour</grapheme>
     <grapheme>color</grapheme>
     <phoneme>ˈkʌlər</phoneme>
     <!-- IPA string is: "&#x2c8;k&#x28c;l&#x259;r" -->
   </lexeme>
 </lexicon>

 <?xml version="1.0" encoding="UTF-8"?>
 <lexicon version="1.0" 
      xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 
        http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"
      alphabet="ipa" xml:lang="jp">
   <!-- Japanese entry showing how multiple writing systems are handled
          romaji, kanji and hiragana orthographies -->
   <lexeme>
     <grapheme>nihongo</grapheme>
     <grapheme>日本語</grapheme>
     <grapheme>にほんご</grapheme>
     <phoneme>ɲihoŋŋo</phoneme>
     <!-- IPA string is: "&#x272;iho&#x14b;&#x14b;o" -->
   </lexeme>
 </lexicon>

Homophones

Most languages have homophones, words with the same pronunciation but different meanings (and possibly different spellings), for instance "seed" and "cede". It is recommended that these be represented as different lexemes.

 <?xml version="1.0" encoding="UTF-8"?>
 <lexicon version="1.0" 
      xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 
        http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"
      alphabet="ipa" xml:lang="en-US">
   <lexeme>
     <grapheme>cede</grapheme>
     <phoneme>siːd</phoneme>
     <!-- IPA string is: "si&#x02D0;d" -->
   </lexeme>
   <lexeme>
     <grapheme>seed</grapheme>
     <phoneme>siːd</phoneme>
     <!-- IPA string is: "si&#x02D0;d" -->
   </lexeme>
 </lexicon>

Homographs

Most languages have words with different meanings but the same spelling (and sometimes different pronunciations), called homographs. For example, in English the word bass (fish) and the word bass (in music) have identical spellings but different meanings and pronunciations. Although it is recommended that these words be represented using separate <lexeme> elements that are distinguished by different values of the role attribute (see Section 4.4 of PLS 1.0), if a pronunciation lexicon author does not want to distinguish between the two words they could simply be represented as alternative pronunciations within the same <lexeme> element. In the latter case the TTS processor will not be able to distinguish when to apply the first or the second transcription.

In this example the pronunciations of the homograph "bass" are shown.

 <?xml version="1.0" encoding="UTF-8"?>
 <lexicon version="1.0" 
      xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 
        http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"
      alphabet="ipa" xml:lang="en-US">
   <lexeme>
     <grapheme>bass</grapheme>
     <phoneme>bæs</phoneme>
     <!-- IPA string is: b&#x00E6;s -->
     <phoneme>beɪs</phoneme>
     <!-- IPA string is: be&#x026A;s -->
   </lexeme>
 </lexicon>

Note that English contains numerous examples of noun-verb pairs that can be treated either as homographs or as alternative pronunciations, depending on author preference. Two examples are the noun/verb "refuse" and the noun/verb "address".

 <?xml version="1.0" encoding="UTF-8"?>
 <lexicon version="1.0" 
      xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 
        http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"
      xmlns:mypos="http://www.example.org/my_pos_namespace"
      alphabet="ipa" xml:lang="en-US">
   <lexeme role="mypos:verb">
     <grapheme>refuse</grapheme>
     <phoneme>rɪˈfjuːz</phoneme>
     <!-- IPA string is: "r&#x026A;&#x02C8;fju&#x02D0;z" -->
   </lexeme>
   <lexeme role="mypos:noun">
     <grapheme>refuse</grapheme>
     <phoneme>ˈrefjuːs</phoneme>
     <!-- IPA string is: "&#x02C8;refju&#x02D0;s" -->
   </lexeme>
 </lexicon>

Pronunciation by Orthography (Acronyms, Abbreviations, etc.)

For some words and phrases pronunciation can be expressed quickly and conveniently as a sequence of other orthographies. The developer is not required to have linguistic knowledge, but instead makes use of the pronunciations that are already expected to be available. To express pronunciations using other orthographies the <alias> element may be used.

This feature may be very useful to deal with acronym expansion.

 <?xml version="1.0" encoding="UTF-8"?>
 <lexicon version="1.0" 
      xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 
        http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"
      alphabet="ipa" xml:lang="en-US">
   <!-- 
     Acronym expansion
   -->
   <lexeme>
     <grapheme>W3C</grapheme>
     <alias>World Wide Web Consortium</alias>
   </lexeme>
   <!-- 
     number representation
   -->
   <lexeme>
     <grapheme>101</grapheme>
     <alias>one hundred and one</alias>
   </lexeme>
   <!-- 
     crude pronunciation mechanism
   -->
   <lexeme>
     <grapheme>Thailand</grapheme>
     <alias>tie land</alias>
   </lexeme>
   <!-- 
     crude pronunciation mechanism and acronym expansion
   -->
   <lexeme>
     <grapheme>BBC 1</grapheme>
     <alias>be be sea one</alias>
   </lexeme>
 </lexicon>

Status and Future

PLS 1.0 reached the status of W3C Recommendation on 14 October 2008.

References

PLS Specification (W3C Recommendation)

External links

World Wide Web Consortium (W3C)

Products and
standards

Recommendations	ARIA Canonical XML CDF CSS DOM Geolocation API HTML (HTML5) ITS MathML OWL P3P PLS RDF RDF Schema SISR SKOS SMIL SOAP SRGS SRI SSML SVG SCXML SPARQL Timed text VoiceXML Web storage WSDL XForms XHTML XHTML+RDFa XInclude XLink XML XML Base XML Encryption XML Events XML Information Set XML namespace XML Schema XML Signature XOP XPath XPath 2.0 XPointer XProc XQuery XSL XSL-FO XSLT (elements)

Notes	XAdES XHTML+SMIL XUP

Working drafts	CCXML CURIE EME InkML JSON-LD MSE RIF SMIL Timesheets sXBL WICD XFDL XFrames XBL XMLHttpRequest

Guidelines	Web Content Accessibility Guidelines

Initiative	Multimodal Interaction Activity (MMI) Markup Validation Service Web Accessibility Initiative WebPlatform

Deprecated	C-HTML HDML JSSS PGML VML XHTML+MathML+SVG

Organizations

Advisory Committee (AC) World Wide Web Foundation

Elected groups	Advisory Board (AB) Technical Architecture Group (TAG)

Working groups	CSS HTML Geolocation Social Web SVG Web Hypertext Application Technology (WHATWG) Web Platform

Closed groups	Device Description (DDWG) WebOnt (Semantic Web Activity)

Software

CERN httpd Libwww

Browsers	Line Mode (1990–) Arena (1993–98) Agora (1994–97) Argo (1994–97) Amaya (browser/editor, 1996–2012)

Conferences

International World Wide Web Conference (IW3C)
- Steering Committee (IW3C2)
- First conference ("WWW1", 1994)

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