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The W3C Voice Browser Working Group aims to develop specifications to enable access to the Web using spoken interaction. This document is part of a set of requirements studies for voice browsers, and provides details of the requirements for markup used for specifying application specific pronunciation lexicons.
Application specific pronunciation lexicons are required in many situations where the default lexicon supplied with a speech recognition or speech synthesis systemprocessor does not cover the vocabulary of the application. A pronunciation lexicon is a collection of words or phrases together with their pronunciations specified using an appropriate pronunciation alphabet.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. The latest status of this document series is maintained at the W3C.A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This document describes the requirements for markup used for pronunciation lexicon, as a precursor to starting work on Speech Interface Framework. This new requirements list replaces the old requirements. New requirements are now in line with VoiceXML 2.0 Recommendation, and other Voice Browser Working Group specification requirements. Changes between these two versions are described in a diff document. You are encouraged to subscribe to the public discussion list <email@example.com> and to mail us your comments. To subscribe, send an email to <www-voice-request@w3. org> with the word subscribe in the subject line (include the word unsubscribe if you want to unsubscribe). A public archive is available online.
This document has been produced as part of the W3C Voice Browser Activity, following the procedures set out for the W3C Process. The authors of this document are members of the Voice Browser Working Group (W3C Members only).
Patent disclosures relevant to this specification may be found on the Working Group's patent disclosure page. This document has been produced under the 24 January 2002 CPP as amended by the W3C Patent Policy Transition Procedure. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) with respect to this s pecification should disclose the information in accordance with section 6 of the W3C Patent Policy.
Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite W3C Working Drafts as other than "work in progress". A list of current W3C Recommendations and other technical documents can be found at http://www.w3.org/TR.It is inappropriate to cite this document as other than work in progress.
This document establishesThe main goal of this subgroup is to establish a prioritized list of requirements for pronunciation lexicon markup which any proposed markup language should address. This document addresses both procedure and requirements for the specification development. The requirements are addressed in separate sections on Lexicon Requirements, Orthographic Requirements, Pronunciation RepresentationRequirements, and MiscellaneousPronunciation alphabet Requirements, followed by links to Further Reading MaterialFuture Study and Acknowledgements sections.
In voice browsing applications there is often a need to use proper nouns or other unusual words within speech recognition grammars and in text to be read out by Text-to-Speech systemsprocessors. These words may not be present in the platforms' built-in lexicons, in. In such cases voice browsers typically resort to automatic pronunciation generation algorithms, which tend to produce pronunciations of poorer quality thanmay be improved by manually specificied pronunciations. The goal of the pronunciation lexicon markup is to provide a mechanism for application developers to supply high quality additional pronunciations in a platform independent manner.
In many cases application developers will need to only provide one or two additional pronunciations inline within other voice markupsmarkup languages , but there are other cases where an application may make use of large pronunciation lexicalexicons that cannot conveniently be specified inline and will have to be provided as separate documents. The pronunciation lexicon markup will address both communities.
The markup language for pronunciation lexicalexicons will be developed within the following broad design criteria. They are ordered from higher to lower priority. In the event that two goals conflict, the higher priority goal takes precedence. Specific technical requirements are addressed in the following sections.
The pronunciation lexicon markup must be interoperable with other relevant specifications developed by the W3C Voice Browser Working Group. In particular the pronunciation lexicon markup must be compatible with the Speech Synthesis Markup Language [SSML] and, Speech Recognition Grammar MarkupSpecification [SRGS], and the (unpublished) dialog markup language.
It should be possible to embed the pronunciation lexicon markup withinThe pronunciation lexicon markup may be embedded in the Speech Synthesis Markup Language [SSML] and in, Speech Recognition Grammar MarkupSpecification [SRGS], and the (unpublished) dialog markup language.
The pronunciation lexicon markup must support the ability to specify multiple entries within a lexicondocument, each entry containing orthographic, and pronunciation and miscellaneous information.
The pronunciation markup may provide a mechanism to allow the specification of multiple independent pronunciation lexicons within a single document. This may be useful for separating lexicons into application specific classes of pronunciation e.g. all city names
The pronunciation lexicon markup may provide named groupings of lexicon entries within a single lexicon document.This may be useful for separating lexicons into application specific classes of pronunciation e.g. all city names.ISSUE #3: Is this enough?
The pronunciation lexicon markup must provide the ability to specify the pronunciation alphabet for use by all entries within a lexicondocument, such as the phonetic alphabet defined by the International Phonetic Association IPA [IPA].
The pronunciation lexicon markup must support the ability to specify a pronunciation lexicon for a single language within a single document and identify the language of the lexicon.Language identifiers should follow the recommendations of rfc1766 or its successors
The pronunciation lexicon markup must provide the ability to specify language identifiers for use by all entries within a document. Each language identifier must be expressed following RFC 3066 [RFC3066].
The pronunciation lexicon may support the ability to specify language for an individual entry within a lexicon, thereby allowing multilingual entries within a single lexicon.Language identifiers should follow the recommendations of rfc1766 or its successors
The pronunciation lexicon may support the ability to specify language identifiers for an individual entry within a document. Each language identifier must be expressed following RFC 3066 [RFC3066].
The pronunciation lexicon markup may support the ability to import other pronunciation lexicalexicons written in the pronunciation lexicon markup.
The pronunciation markup may support the ability to import lexicon entries from other pronunciation lexiconslexica written in the pronunciation lexicon markup.
To facilitate use of the pronunciation lexicon markup by itself and other markups, a lexicon should be externally addressable through normal URI addressing.
To facilitate use of the pronunciation lexicon entries by itself and other markups, lexicon entries should be externally addressable using URI document fragment identifiers.
The pronunciation lexicon markup should allow control of the interaction of application lexica with built in platform lexica. Examples of possible behaviour include:
The pronunciation lexicon markup should provide a mechanism for specifying metadata within pronunciation lexicon documents. This metadata can contain information about the document itself rather than document content. For example: record the purpose of the lexicon document, the author, etc.ISSUE #4: Do we actually need this requirement if we use metadata in a standard way?
The pronunciation lexicon markup shouldmust allow multi word orthographies. This is particularly important for natural speech applications where common phrases may have significantly different pronunciations to that of the concatenated word pronunciations, requiring a phrase level pronunciation. An example would be "how about" often pronounced "how 'bout".
The pronunciation lexicon markup must provide the ability to indicate an alternative equivalent form of the orthography.
This is required to cover the following situations:
It must also be possible to provide additional information to indicate the "type" of the alternate pronunciation, though this specification may not define a standard set of "types"
See also related requirement: 4.4Handling of homographs.
The pronunciation lexicon markup should provide a mechanism to indicate the broad syntactic category of the orthography, e.g. noun, verb, pronoun etc. Required to enable recognisers and/or synthesizers to select the lexicon entry appropriate for the context.The markup may define these categories. These categories may be based upon existing standards such as EAGLES
The pronunciation lexicon markup must provide a mechanism for lexicon developers to associate miscellaneous additional information with an orthography, for example to store more detailed syntactic/part-of-speech tags.
In some situations lexicon entries will be explicitly addressed from other voice markups, however at other times markups may import entire pronunciation lexicon documents. In these cases the voice browser will need to lookup and match words within, for example, the Speech Synthesis Markup Language [SSML] and Speech Recognition Grammar MarkupSpecification [SRGS] against the orthographies present in the lexicon. It is likely that a certain degree of textual variability will need to be allowed in order to ensure that the pronunciation lexicon is useful.
The pronunciation lexicon markup specification must make a statement aboutprovide a mechanism to indicate the allowable textual variability in the orthography. Types of variability include, but are not limited to,
The definition of a standard text normalisation scheme is beyond the scope of this specification.
The pronunciation lexicon markup specification mustmay provide a mechanism to deal with the problem of specifying homographs, (words with the same spelling -, but potentially different meanings and pronunciations), within the same lexicondocument.
The pronunciation lexicon markup must provide the ability to specify a single pronunciation for a given lexicon entry as a sequence of symbols according to the pronunciation alphabet selected.
The pronunciation lexicon markup must support the ability to specify multiple pronunciations for a given lexicon entry. See also requirement 5.9
The pronunciation lexicon markup may provide a mechanism for
indicating the dialect or language variation
for each pronunciation, as described in
RFC 3066 [RFC3066],
"en-scounse". For example in UK
english Rhotic Irish, London Cockney, North British etc. Such a
mechanism should follow any appropriate recommendations described
in rfc1766 or its
The pronunciation lexicon markup shouldmust enable indication of which pronunciation is the preferred form for use by a speech synthesizer where there are multiple pronunciations for a lexicon entry. The pronunciation lexicon markup language specification shouldmust define the default selection behaviour for the situations where there are multiple pronunciations but no indicated preference.
The pronunciation lexicon markup may allow for relative weightings to be applied to pronunciations. These weightings to indicate the relative importance of the pronunciations within a single lexicon entry. This can be useful for speech recognition systems.
The pronunciation lexicon markup may allow for an indication of pronunciation quality. This can be useful for providers of pronunciation lexica and for users of external lexica such as Onomastica, COMLEX. Examples of such quality levels may include Manually generated and checked, Manually generated, Automatically generated.
The pronunciation lexicon markup may allow for an indication of originating source of the pronunciation. This can be useful for providers of pronunciation lexica.
The pronunciation lexicon markup should allow the specification of the pronunciation of an orthography in terms of other orthographies with previously defined pronunciations, for example, the pronunciation for "W3C" specified as the concatenation of pronunciations of the words "double you three see".ISSUE #7: Note about it is dangerous in case of multiple pronunciations.
The pronunciation lexicon markup may provide the ability to specify a different pronunciation alphabet to be used for each pronunciation of a lexicon entry. For example this would allow a lexicon entry to have two pronunciations for a particular word/phrase, each pronunciation being in a different pronunciation alphabet. This may be useful when merging pronunciation lexicon from different sources. This may also be useful for enabling platform specific optimised pronunciations.
The pronunciation lexicon markup should provide a convenient shorthand mechanism for developers to specify pronunciations for acronyms, such as BT,ATT,MIT etc .
The pronunciation lexicon markup should reuse standard pronunciation alphabetsWe will standardize on at least one existing pronunciation alphabet, such as the phonetic alphabet defined by the International Phonetic Association IPA [IPA]. In particular the pronunciation alphabets recommended by the Pronunciation alphabet sub group. We do not plan of developing a new standard pronunciation alphabet.
The pronunciation alphabet must allow the specification of pronunciations for any language including tonal languages.
The pronunciation alphabet must provide a mechanism for indicating suprasegmental structure such as, word/syllable boundaries, and stress markings. The specification may address other types of suprasegmental structure.
The choice of pronunciation alphabet should take into account the requirements of interoperability between platforms.
The pronunciation alphabet must be computationally easy to transform to other alphabets
The pronunciation lexicon markup may provide a standard mechanism for specifying transformations between pronunciation alphabets
The pronunciation lexicon markup must allow for vendor specific pronunciation alphabets to be used.
The pronunciation lexicon markup should provide guidance on the recommended use of the pronunciation alphabet across languages
The specification must address the issue of compliance by defining the sets of features that must be implemented for a system to be considered compliant with the specification. Where appropriate, compliance criteria may be defined with variants for different contexts or environments.
The pronunciation lexicon markup must support a mechanism for inline comments.
The pronunciation lexicon markup should aim for a compact representation to minimise network bandwith requirements when transferring lexica between server and voice browser. Where this conflicts with the generic requirement for human readibility then readability takes precedence.
The pronunciation lexicon markup should provide a mechanism for specifying meta data within pronunciation lexicon documents. This meta data can contain information about the document rather than document content.
This section contains issues that were identified during requirements capture but which have not been directly incorporated in the current set of requirements.
iIt may be desirable to provide an addressing scheme for lexicon entries that is more flexible than the document and fragment URI schemes currently listed in the requirements. An example of a more powerful addressing mechanism could be XPath.
In some situations the explicit specification of all the
morphological variants of a word can lead to extremely large
lexicons. A standard scheme for providing prefix and suffix
morphological rules would enable more compact lexicons documents. However it
is felt that the most common use of the pronunciation lexicon
markup will be for proper nouns where morphological variance is
markup will be for proper nouns where morphological variance is
less of an issue, and that standardisation of morphological rules
will be too difficult to achieve in a first draft. Off-line tools
may provide mechanisms for generating morphological variants.
In some languages the pronunciation of an orthography and the
orthography itself are dependent upon the context in which this
orthography is used. The requirements do not address this issue. It
may not be possible to resolve this issue in a vendor independent
manner. It is possible that the additional information field could
be used to handle this situation in a platform dependent
In languages such as German and Dutch words can occur as part of compound words and in some cases may only occur within compound words. The requirements do not say how compound words will be handled.In the future, the pronunciation lexicon markup should address handling compound words.
The following resources are related to the Pronunciation Lexicon Markup Language requirements and specification.
The editor wishes to thank the previous author of this document, Frank Scahill, and the old and new members of the pronunciation lexicon subgroup of the W3C Voice Browser Working Group involved in this activity (listed in alphabetical order):