Capturing slot values with spelling styles - Amazon Lex

Capturing slot values with spelling styles

Amazon Lex V2 provides built-in slots to capture user-specific information such as first name, last name, email address or alphanumeric identifiers. For example, you can use the AMAZON.LastName slot to capture surnames such as "Jackson" or "Garcia." However, Amazon Lex V2 may get confused with surnames that are difficult to pronounce or that are not common in a locale, such as "Xiulan." To capture such names, you can ask the user to provide input in spell by letter or spell by word style.

Amazon Lex V2 provides three slot elicitation styles for you to use. When you set a slot elicitation style, it changes the way Amazon Lex V2 interprets the input from the user.

Spell by letter – With this style, you can instruct the bot to listen for spellings instead of the whole phrase. For example, to capture a last name such as "Xiulan," you can tell the user to spell out their last name one letter at a time. The bot will capture the spelling and resolve the letters to a word. For example, if the user says "x i u l a n," the bot captures the last name as "xiulan."

Spell by word – In voice conversations, especially using the telephone, there are a few letters, such as "t," "b," "p", that sound similar. When capturing alphanumeric values or spelling names results in an incorrect value, you can prompt the user to provide an identifying word along with the letter. For example, if the voice response to a request for a booking ID is "abp123," your bot might instead recognize the phrase "abb123" instead. If this is an incorrect value, you can ask the user to provide the input as "a as in alpha b as in boy p as in peter one two three." The bot will resolve the input to "abp123."

When using spell by word, you can use the following formats:

  • "as in" (a as in apple)

  • "for" (a for apple)

  • "like" (a like apple)

Default – This is the natural style of slot capture using word pronunciation. For example, it can capture names such as "John Stiles" naturally. If a slot elicitation style isn't specified, the bot uses the default style. For the AMAZON.AlphaNumeric and AMAZON.UKPostal code slot types, the default style supports spell by letter input.

If the name "Xiulan" is spoken using a mix of letters and words , such as "x as in x-ray i u l as in lion a n" the slot elicitation style must be set to spell-by-word style. The spell-by-letter style won't recognize it.

You should create a voice interface that captures slot values with natural conversational style for a better experience. For inputs that are not correctly captured using the natural style, you can re-prompt the user and set the slot elicitation style to spell-by-letter or spell-by-word.

You can use spell-by-word and spell-by-letter styles for the following slot types in the English (US), English (UK), and English (Australia) languages:

Enabling spelling

You enable spell-by-letter and spell-by-word at runtime when you are eliciting slots from the user. You can set the spelling style with the PutSession, RecognizeText, RecognizeUtterance, or StartConversation operation. You can also enable spell-by-letter and spell-by-word using a Lambda function.

You set the spelling style using the dialogAction field of the sessionState field in the request of one of the aforementioned API operations or when configuring the Lambda response (see Preparing the response format for more information). You can only set the style when the dialog action type is ElicitSlot and when the slot to elicit is one of the supported slot types.

The following JSON code shows the dialogAction field set to use the spell-by-word style:

"dialogAction": { "slotElicitationStyle": "SpellByWord", "slotToElicit": "BookingId", "type": "ElicitSlot" }

The slotElicitationStyle field can be set to SpellByLetter, SpellByWord, or Default. If you don't specify a value, then the value is set to Default.


You can't enable spell-by-letter or spell-by-word elicitation styles through the console.

Example code

Changing the spelling style is usually performed if the first attempt to resolve a slot value that didn't work. The following code example is a Python Lambda function that uses the spell-by-word style on the second attempt to resolve a slot.

To use the example code, you must have:

  • A bot with one language, English (GB) (en_GB).

  • One intent, "CheckAccount" with one sample utterance, "I would like to check my account". Make sure that Use a Lambda function for initialization and validation is selected in the Code hooks section of the intent definition.

  • The intent should have one slot, "PostalCode", of the AMAZON.UKPostalCode built-in type.

  • An alias with the Lambda function defined. For more information, see Creating and attaching a Lambda function to a bot alias.

import json import time import os import logging logger = logging.getLogger() logger.setLevel(logging.DEBUG) # --- Helpers that build all of the responses --- def get_slots(intent_request): return intent_request['sessionState']['intent']['slots'] def get_session_attributes(intent_request): sessionState = intent_request['sessionState'] if 'sessionAttributes' in sessionState: return sessionState['sessionAttributes'] return {} def get_slot(intent_request, slotName): slots = get_slots(intent_request) if slots is not None and slotName in slots and slots[slotName] is not None: logger.debug('resolvedValue={}'.format(slots[slotName]['value']['resolvedValues'])) return slots[slotName]['value']['resolvedValues'] else: return None def elicit_slot(session_attributes, intent_request, slots, slot_to_elicit, slot_elicitation_style, message): return {'sessionState': {'dialogAction': {'type': 'ElicitSlot', 'slotToElicit': slot_to_elicit, 'slotElicitationStyle': slot_elicitation_style }, 'intent': {'name': intent_request['sessionState']['intent']['name'], 'slots': slots, 'state': 'InProgress' }, 'sessionAttributes': session_attributes, 'originatingRequestId': 'REQUESTID' }, 'sessionId': intent_request['sessionId'], 'messages': [ message ], 'requestAttributes': intent_request['requestAttributes'] if 'requestAttributes' in intent_request else None } def build_validation_result(isvalid, violated_slot, slot_elicitation_style, message_content): return {'isValid': isvalid, 'violatedSlot': violated_slot, 'slotElicitationStyle': slot_elicitation_style, 'message': {'contentType': 'PlainText', 'content': message_content} } def GetItemInDatabase(postal_code): """ Perform database check for transcribed postal code. This is a no-op check that shows that postal_code can't be found in the database. """ return None def validate_postal_code(intent_request): postal_code = get_slot(intent_request, 'PostalCode') if GetItemInDatabase(postal_code) is None: return build_validation_result( False, 'PostalCode', 'SpellByWord', "Sorry, I can't find your information. " + "To try again, spell out your postal " + "code using words, like a as in apple." ) return {'isValid': True} def check_account(intent_request): """ Performs dialog management and fulfillment for checking an account with a postal code. Besides fulfillment, the implementation for this intent demonstrates the following: 1) Use of elicitSlot in slot validation and re-prompting. 2) Use of sessionAttributes to pass information that can be used to guide a conversation. """ slots = get_slots(intent_request) postal_code = get_slot(intent_request, 'PostalCode') session_attributes = get_session_attributes(intent_request) if intent_request['invocationSource'] == 'DialogCodeHook': # Validate the PostalCode slot. If any aren't valid, # re-elicit for the value. validation_result = validate_postal_code(intent_request) if not validation_result['isValid']: slots[validation_result['violatedSlot']] = None return elicit_slot( session_attributes, intent_request, slots, validation_result['violatedSlot'], validation_result['slotElicitationStyle'], validation_result['message'] ) return close( intent_request, session_attributes, 'Fulfilled', {'contentType': 'PlainText', 'content': 'Thanks' } ) def close(intent_request, session_attributes, fulfillment_state, message): intent_request['sessionState']['intent']['state'] = fulfillment_state return { 'sessionState': { 'sessionAttributes': session_attributes, 'dialogAction': { 'type': 'Close' }, 'intent': intent_request['sessionState']['intent'], 'originatingRequestId': 'xxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx' }, 'messages': [ message ], 'sessionId': intent_request['sessionId'], 'requestAttributes': intent_request['requestAttributes'] if 'requestAttributes' in intent_request else None } # --- Intents --- def dispatch(intent_request): """ Called when the user specifies an intent for this bot. """ intent_name = intent_request['sessionState']['intent']['name'] response = None # Dispatch to your bot's intent handlers if intent_name == 'CheckAccount': response = check_account(intent_request) return response # --- Main handler --- def lambda_handler(event, context): """ Route the incoming request based on the intent. The JSON body of the request is provided in the event slot. """ # By default, treat the user request as coming from # Eastern Standard Time. os.environ['TZ'] = 'America/New_York' time.tzset() logger.debug('event={}'.format(json.dumps(event))) response = dispatch(event) logger.debug("response={}".format(json.dumps(response))) return response