An ABNF Primer

An ABNF PrimerConcepts, 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.

Structure of an ABNF Grammar
Headers
#ABNF 1.0 ISO-8859-1;
language en-US;
mode voice;
root$yesOrNo;
private$yesOrNo =
yes {out.value = 'yes'}
| no {out.value = 'no'}
;
Rules

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/>;

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

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

http://blog.nuecho.com	293
http://www.grammarserver.com	284
http://nugram.nuecho.com	200
http://grammarserver.com	29
https://www.grammarserver.com	7
http://translate.googleusercontent.com	2
http://translate.googleusercontent.com	2
http://centos:8104	1
http://lelouch.nuecho.ad:8104	1

An ABNF Primer

by Nu Echo Inc. on Jul 15, 2010

Accessibility

Categories

Tags

Upload Details

Usage Rights

9 Embeds 819

Statistics

An ABNF Primer — Presentation Transcript