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 lexica.
Application specific pronunciation lexica are required in many situations where the default lexicon supplied with a speech recognition or speech synthesis system 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.
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This document describes the requirements for markup used for pronunciation lexica, as a precursor to starting work on Speech Interface Framework. You are encouraged to subscribe to the public discussion list <firstname.lastname@example.org> 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).
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.
The 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 Representation and Miscellaneous followed by links to Further Reading Material.
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 systems. These words may not be present in the platforms built-in lexicons, in such cases voice browsers typically resort to automatic pronunciation generation algorithms which tend to produce pronunciations of poorer quality than 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 markups , but there are other cases where an application may make use of large pronunciation lexica 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 lexica 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, Speech Recognition Grammar Markup, and the (unpublished) dialog markup language.
It should be possible to embed the pronunciation lexicon markup within theSpeech Synthesis Markup, Speech Recognition Grammar Markup and the (unpublished) dialog markup language.
The pronunciation lexicon markup must support the ability to specify multiple entries within a lexicon, each entry containing orthographic, 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 must provide the ability to specify the pronunciation alphabet for use by all entries within a lexicon
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 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 markup may support the ability to import other pronunciation lexica written in the pronunciation lexicon markup.
The pronunciation markup may support the ability to import lexicon entries from other pronunciation lexica 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 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: Handling 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 and Speech Recognition Grammar Markup 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 about 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 must provide a mechanism to deal with the problem of specifying homographs, same spelling - potentially different meaning and pronunciation, within the same lexicon
The pronunciation 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 for each pronunciation. 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 successors.
The pronunciation lexicon markup should 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 markup language specification should 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"
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 alphabets. In particular the pronunciation alphabets recommended by the Pronunciation alphabet sub group.
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.
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.
The following resources are related to the Pronunciation Lexicon Markup Language requirements and specification.
The editor wishes to thank the members of the pronunciation lexicon subgroup of the Voice Browser working group: