Speech Recognition Grammars

7/29/2019 Speech Recognition Grammars

1/35

VoiceXML:

Speech Recognition Grammars


2/35

Acknowledgements

Prof. Mctear, Natural Language Processing,http://www.infj.ulst.ac.uk/nlp/index.html, University ofUlster.

Bevocal documentation
http://www.infj.ulst.ac.uk/nlp/index.htmlhttp://www.infj.ulst.ac.uk/nlp/index.html


3/35

Overview

Types of grammar Grammar design and use

Optional items in a grammar

Semantic tags

DTMF grammars

Grammar rules

Built-in grammars

Grammar scope
http://localhost/var/www/apps/conversion/Voice%20demos/speechreco.exe


4/35

What is a grammar

A grammar defines the words and patterns of words that a user cansay at any particular point in a dialogue

Uses:

speech recognition: to constrain the speech recognition process byspecifying permissible sequences of words

language understanding: to determine the structure and/or

meaning of a sequence of words e.g.Transfer one hundred dollars from my checking to my savingsaccount

might be parsed and transformed into the structure:

transfer

savings

checking

100


5/35

Types of grammar

Finite-state and phrase structure take the form of rules with a left-hand and right-hand side

e.g.noun_phrase -> determiner adjective noun

flight ->

used in language understanding and speech recognition

N-gram (used in speech recognition)

based on probabilities of word combinationse.g. bigrams, trigrams


6/35

Grammar in VoiceXML

May be specifiedInline i.e. embedded into a VoiceXML page External i.e. stored as files on Web servers, etc.

Grammar formats XML, ABNF (Augmented BNF syntax), Java Speech

Grammar format (JSGF), GSL (Nuances GrammarSpecification language) W3C specification embodies XML and ABNF IBM Voice Toolkit supports the XML and ABNF grammar

formats Bevocal Caf, Voxpilot and Tellme support the XML and

GSL grammar formats For further details on the W3C Speech Recognition

Grammar Specification, seehttp://www.w3.org/TR/speech-grammar/
http://www.w3.org/TR/speech-grammar/http://www.w3.org/TR/speech-grammar/http://www.w3.org/TR/speech-grammar/http://www.w3.org/TR/speech-grammar/


7/35

Inline and External Grammar Definitions

An inline grammar is definedwithin the elementin a VoiceXML document.

In an inline grammar, if thegrammar consists of exactly 1rule, that rule does not have tohave a name.

GSL grammars use specialcharacters: wrap your inlinegrammar as a section ofCDATA:

An external grammar is defined in

an external file and referenced inthe VoiceXML document

In an external grammardocument, all rules must benamed

In external GSL grammar file, thecontents of that file should notbeinside a CDATA section andshould not contain a element. :

;GSL2.0 ...grammar ruledefinitions...


8/35

element

Specifies a set of possible responses for a field If the number of possible responses is small, then a setof elements can be used instead of a element


9/35

Grammar Design

A grammar should cover all the ways that a user might say

something

1. Alternative choices within a category e.g.studentname [john rosemary etc]

2. Alternative words for the same concept e.g.[comms communications]

3. Alternative sentences that have the same meaning e.g.[(student john scott taking databases)(databases john scott)(john scott taking the course databases)]

Note: careful wording of prompts can constrain the user tosaying what has been predicted by the grammar designer

These examples use the GSL grammar format,

which is more suitable than the XML format forthe presentation of examples


10/35

Grammars for words

Simplewords (or

touch-tonestrings):tokens

GSL

(student name)

XML

student name

Alternativewords

GSLChoice[

students

courses

reports]

XML


11/35

Making items optional

GSLName

(?firstname lastname)

XML


12/35

Making items optional-2

( [ news weather sports ] ?please )

( ?[ (i'd like) (tell me) ] ?the [ news weather sports ]?please )


13/35

Repeating items

XML: repeat = "0-1" means the item is optional i.e. zero or one

time

repeat = "n- means the item is repeated n or more timese.g. 0- = zero or more times

repeat = "m-n" means the item re repeated between mand ntimes (inclusive) e.g. 1-3 = between one and threetimes

repeat = "n" means the item is repeated exactly n times GSL:

+(item) - the item is repeated 1 or more times *(item) - the item is repeated 0 or more times

?(item) the item is optional


14/35

Grammar Slots (Tags)

Grammar slots are used in grammars to return a valuerepresenting the meaning of the word(s) recognised e.g.

checking account and checking should return the samevalue.

GSL:


15/35

Grammars often consist of sub-grammars e.g.

;GSL 2.0;

ColoredOjbect:public (Color Object)

Color [

[red pink] { }[yellow canary] { }

[green khaki] { }

]

Object [

[truck car] { }[ball block] { }

[shirt blouse] { }

]

"yellow shirt" "canary blouse"=> { color: yellow; object: clothing; }

Grammar rules: sentences

Colored Object

ObjectColor


16/35

Grammar with sub-rules

Sub-grammars and rules are referenced in XML form using arule reference. A rule reference can point to a localgrammar, or an external grammar rule contained in anotherfile or even on another server on the Internet.

Design of a grammar consisting of sub-grammars requiresconsiderable planning to ensure that all possible utterancesare covered and also to avoid redundancies as well asrepetitions in the grammar.

It is often useful to map out the grammar diagrammatically or

using a simple format such as GSL or ABNF beforeattempting to code the rules in XML format.


17/35

Rule Scope - GSL

Each defined rule has a scope of either private or public. A rule withpublicscope is

visible outside its grammar and can be referenced by name from othergrammars can be activated for recognition (can serve as a top-level rule)

A rule withprivate scope is visible only within its containing grammar may be referenced only by other rules within the same grammar.

To mark a rule as public, the format is: RuleName:public ruleExpansion If no rules in the grammar are explicitly marked with :public, then all

rules in the grammar are public. If any rule in the grammar is marked with :public, then all public rules

must be so marked. The root rule in a GSL grammar is always the first public rule.

For example, the following set of definitions creates one public rule namedSnapperand two private rules named SnapperType and FishColors:

SnapperType [mutton FishColors]FishColors [black gray red]Snapper:public (SnapperType snapper)


18/35

Rule scope - XML By default, VoiceXML 2.0 grammar rules are private. This

means that the rules can only be referenced within the same

grammar file. To allow a grammar rule to be referenced from an external

source, such as a VoiceXML document or another grammar,the rule needs to be scoped as public using the scopeattribute


19/35

Grammar Headers - GSL

Inline

External:;GSL2.0

...grammar rule definitions...

No definition of top-level rule

Referencing an external grammar or a top level rule in agrammar:


20/35

Grammar Headers - XMLInline


21/35

Grammar Scope

Grammar elements can be included within anyVoiceXML element that receives user input field link: for transitions to other documents e.g. operator.vxml menu: grammar implicitly specified by the

element form: for mixed-initiative dialogues

by default the scope of a grammar is limited to theelements in which it is defined

scope can be set using the scope attribute e.g.

grammars defined within forms or menus can be givendocument scope grammars defined in the root document scope to the

entire application


22/35

Using Grammar Effectively

A grammar should cover effectively the range ofresponses that can be encountered to a prompt

this can include the essential input as well asextraneous words and phrases

a grammar that is too large will hinder speechprocessing and lead potentially to more misrecognitions

scope is important: grammars should not overlap

excessive use of global grammars (defined in the root

document) can increase the possibility of overlapping


23/35

Tutorial Exercise 1. Using tagsIntegrate the following rule and its grammar into an application thattakes in the name of a student and the name of a course and outputs

the student's name along with a course code.

comms communications $="01"

algorithms $="02" programming $="03" databases $="04"


24/35

DTMF

DTMF (touch-tone) can be used as an alternative to speechinput, particularly when speech recognition is unreliable orproblematic.

In VoiceXML 2.0 dtmf is included as a value of the modeattribute in the element

1 $= students" 2 $= courses"

3 $= reports"


25/35

DTMF and / or speech in GSL

;GSL 2.0;

Rating(

?[(i feel ?like) (it is ?a) (its ?a)][

[one dtmf-1] { }

[two dtmf-2] { }

[three dtmf-3] { }

.

]


26/35

DTMF after counts

Prompt counts can be used, e.g. to give the user anopportunity to choose using speech, then advise use of

keypad if speech is unsuccessful

please use your keypad


27/35

Tutorial Exercise 2: DTMF and speech

Create a file with choices (student details | course details | reports)

that allows speech as well as DTMF inputInclude a nomatch (or noinput) event that asks the user to use the

keypad on the second time that speech input is unsuccessful.

The system should confirm with words rather than DTMF

1 $= "student details"

student details $= "student details"


28/35

Built-In Grammars

Built-in grammars are provided in VoiceXML boolean (true or false: in DTMF 1 is true, 2 is false)

date

digits (e.g. three four seven)

currency number (e.g. three hundred and forty seven)

phone

time

specifying within the element


29/35

Built-In Grammar: Digits

Digit recognition is performed in VoiceXML by using a built-in grammar

for digits that is declared as a field type. For example:


30/35

Digits grammar example


31/35

Built-in grammar: boolean

The boolean grammar contains ways of saying yes or no

The particular words within the boolean grammar aredependent on the locale i.e. the language type e.g. USEnglish, UK English, etc.

The words may also vary from one platform to another

IBM Voice Toolkit UK English:

yes, true, positive, right, ok, sure, affirmative, check, yep,correct, no, false, negative, wrong,not, nope, incorrect

The return value sent is a boolean true or false.

If the field name is subsequently used in a value elementwithin a prompt, the TTS engine will speak eitheryes orno.

Users can also provide DTMF input: 1 is yes, and 2 is no.


32/35

Boolean grammar example


33/35

Built-in field type Sample input

currency three twenty five

sixteen dollars and fifty seven centsten dollars

nine million two hundred thousand dollars

date may fifth

march

the thirty first of december two thousandyesterday

today

tomorrow

phone seven three five eight four nine zero

two one two four nine six two seven oh six

Sample input for built-in field types


34/35

Built-in field type Sample input

number ten million five hundred thousand and fifty

three

minus one point five

plus one point five

point seven

digits zero, oh, one, two, three, four , five, six,

seven, eight, nine

time one oclock

five past one

three fifteen

seven thirty

half past eight

oh four hundred hours

sixteen fifty

twelve noon

midnight

Sample input for UK English built-in field types (continued)


35/35

Tutorial Exercise 3. Built-in grammars

Aim: to include built-in grammars

Create an application in which the user has to speak theiraccount number, which consists of 6 digits (use built-indigit grammar).

Extend the application with other built-in grammars, suchas date.

Experiment with the use of the DTMF simulator to enterthe values for account number, date, etc.

Documents

Speech Recognition Grammars