An ABNF Primer

An ABNF Primer

Concepts, structure, syntax

Introduction

• W3C standard– http://www.w3.org/TR/speech-grammar– W3C recommandation:

• March 16th, 2004– Defines both the XML form and the Augmented BNF (ABNF)

form • They are equivalent

• Supported by a complete development environment• NuGram IDE

Copyright © 2010 Nu Echo Inc.

http://www.w3.org/TR/speech-grammar

http://nugram.nuecho.com/product_app/nugram_ide

http://nugram.nuecho.com/product_app/nugram_ide

Structure of an ABNF Grammar

#ABNF 1.0 ISO-8859-1;language en-US;mode voice;root $yesOrNo;

private $yesOrNo = yes {out.value = 'yes'} | no {out.value = 'no'};

Rules

Headers


Comments

• C/C++/Java Comments– // to end of line– /* ... */

• Documentation comments– /** ... */– @example to document sample sentences– Can appear before rule definitions, root header, and language

header.


GRAMMAR HEADERS


Grammar Headers

• Self-identifying header– Mandatory– Encoding is optional– Can be preceded by byte order mask (BOM)

Ex:#ABNF 1.0;#ABNF 1.0 UTF-8;


Grammar Headers

• Language– Identifies the language of the document– Required for voice grammars– Languages codes defined by RFC 3066

Ex:language en;language fr-CA;


Grammar Headers

• Mode– Indicates the type of input– Optional header– 'dtmf' or 'voice' (default)

Ex:mode voice;mode dtmf;


Grammar Headers

• Root– Defines the grammar's top-level rule– Optional– Root rule can be either public or private

Ex:root $rootRule;


Grammar Headers

• Tag-format– Declares content type for the semantic tags (actions)– Value is a URI– Recognition-engine specific

Ex:tag-format <semantics/1.0>; (SISR)tag-format <Nuance>; (Nuance)tag-format <swi-semantics/1.0>; (Nuance)tag-format <semantics-ms/1.0>; (Microsoft)tag-format <semantics/1.0.2006>; (LumenVox)


Grammar Headers

• Lexicon– Specifies a pronunciation lexicon to use (a URI)– One or more occurrences – Format is engine-specific

Ex:lexicon <../lex/names.pls>;


Grammar Headers

• Base URI– Base URI for all relative URIs in the document– Optional– Has precedence over the meta header

Ex:base <http://localhost:8080/>;


http://localhost:8080/

Grammar Headers

• Meta and Http-Equiv– Metadata attached to the grammar– Properties taking precedence over HTTP headers– One or more occurrences

Ex:meta “Author” is “J. Doe”;http-equiv “Expires” is “0”;


Relative URI Resolving

• Base URI :– base header– meta “base” header – metadata from protocol interaction (ex. HTTP header)– base URI of the current document

Ex:meta “base” is “http://example.com/grammars/date.abnf”;

meta “base” is “http://example.com/grammars/”;

base “http://example.com/grammars/date.abnf”;


Relative URI Resolving

• ASR Engines behave differently

• OSR / Nuance 9 • Full conformance to RFC 2396 (now obsoleted by RFC 3986)

• Loquendo ASR• Base URI must not contain the document’s name

• Best practice: always end the URI with a “/”


GRAMMAR RULES


Grammar Rules

• A rule is an association between a name and an expansion– Rule names are unique in a grammar– Rules can be either public or private

• A public rule is visible outside the scope of the grammar document• A rule is private by default

• An expansion describes a set of word sequences (sentences)


Grammar Rules

• Syntax of a rule definition:

public $name = expansion;or

private $name = expansion;or

$name = expansion;


Rule names

• A rule name must be a valid XML Name– http://www.w3.org/TR/2000/REC-xml-20001006#NT-Name

• But:– Cannot be NULL, VOID, GARBAGE– Must not contain '.', ':', '-'

• Rule names begin with '$'– Ex: $number $names $digits


http://www.w3.org/TR/2000/REC-xml-20001006

BASIC EXPANSIONS


Expansions

• Words (aka tokens)– A string that the recognizer can convert to a phonetic

representation– Typically a word in the specified language– Words are delimited by whitespaces, and

$, <, >, (, ), /, |, [, ], {, }, !– Can be enclosed in “”


Expansions

• Words (cont'd)– Examples:

• hello• Montréal• trente-deux• “San Francisco”


Expansions

• Words (cont'd)– Tips:

• Avoid acronyms, like “IBM” (unless word is in the dictionary)Separate each letter with a “.” or “_”.

– Good: “I.B.M.”, “I triple E”– Bad: “IBM”, “IEEE”

• Don't use abbreviations. – Replace “Dr.” with “Doctor”, “St.” with “street"

• Use spelled forms for numbers– Use “One hundred” instead of “100”


Expansions

• Sequences– Whitespace-separated expansions– Each expansion must match in turn

Ex: I would like to $day $month $year


Expansions

• Choices– To match one of a number of choices– Expansions separated by '|'

Ex: one | two | three | four

$yes | $no {answer = 'no'}


Expansions

• Grouping– Parentheses group expansions (as do square brackets)– Enables encapsulation– Useful to ensure correct precedence in parsing a group of

expansions

Ex:no (it's | it is) not(oh | zero) { out = '0'}


Expansions

• Rule References– References to named expansions– Three types:

• Local references• External references• Special rule names


Expansions

• Local rule references– References to rules declared in the same document

Ex: $date $civicNumber $digit


Expansions

• External rule references– Implicit

• Uses root rule• Root rule can be either public or private$<documentURI>

– Explicit• Rule must be declared public$<documentURI#ruleName>

– Media type can be specified:$<documentURI#ruleName>~<mediatype>


Expansions

• External rule references (cont'd)

Ex:$<../common/numbers.abnf>

$<../common/numbers.abnf#oneToNine>

$<http://localhost:8800/names.abnf?id=45>

$<names.abnf?id=45>~<application/srgs+xml>


Expansions

• Special rule references– $NULL

• matches automatically• equivalent to ()

– $VOID• matches nothing

– $GARBAGE• matches anything• implementation-specific behavior


ADVANCED EXPANSIONS


Expansions

• Repeats– Force the repetition of an expansion– Bounded: <n-m> or <n>– Unbounded: <n->

Ex:$digit <7> | $digit <10>$topping <1->


Expansions

• Repeats (cont'd)– Special case: [ E ]

– Equivalent to E <0-1>– Or to ( E | $NULL )

Ex:$hesitation = [euh] ok [euh];$date = $month [$year];


Expansions

• Repeats (cont'd)– The probability of the repetition can be specified– Syntax: <n-m /prob/>– prob is value between 0.0 and 1.0

Ex: $digit <2-4 /0.8/> $topping <1- /0.785/>


Expansions

• Choices – Weighting– Multiplying factor attached to a choice

• Positively biased when weight > 1.0• Negatively biased when weight < 1.0

– Default weight is 1.0– Syntax: /n./ or /n.n/ or /.n/ or /n/

Ex:(/1.7/ New York | /0.4/ Newark)


Expansions

• Language– Overrides the default language– Applies to all words of the target expansion– Syntax: E!code

Ex:yes | oui!fr-CA(Michel Tremblay|André Roy)!fr-CA


Expansions

• Tags– To attach “meaning” to a sentence– Arbritrary strings enclosed in {}– Content depends on value of the tag-format header

Ex: (two | second) {out.day = 1} $number {val = number.val}


Expansions

• Tags (cont'd)– Use {!{ ... }!} when tag must contain '}'.– Can appear as grammar header

• must be followed by ';‘• Ideal for defining global functions or data structures


Precedence

Priority Expansions

1 Rule reference, token (quoted or unquoted), tag

2 Parentheses and square brackets

3 Repeat operator and language attachment

4 Sequence

5 Choices


Date post:	20-Aug-2015
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An ABNF Primer

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