Creating a custom vocabulary to improve speech recognition - Amazon Lex

Creating a custom vocabulary to improve speech recognition

You can give Amazon Lex V2 more information about how to process audio conversations with a bot by creating a custom vocabulary in a specific language. A custom vocabulary is a list of specific phrases that you want Amazon Lex V2 to recognize in the audio input. These are generally proper nouns or domain-specific words that Amazon Lex V2 doesn't recognize.

For example, suppose that you have a tech support bot. You can add "backup" to a custom vocabulary to help the bot transcribe the audio correctly as "backup," even when the audio sounds like "pack up." A custom vocabulary can also help recognize rare words in the audio such as "solvency" for financial services or proper nouns such as "Cognito" or "Monitron."

Custom vocabulary basics

  • A custom vocabulary works on the transcription of audio input to a bot. You must provide sample utterances to recognize an intent or slot value.

  • A custom vocabulary is unique to a specific language. You must configure custom vocabularies independently for each language. Custom vocabularies are supported only for the English (UK) and English (US) languages.

  • Custom vocabularies support only 8 kHz audio input. It is available with contact center integrations supported by Amazon Lex V2. The test window in the Amazon Lex V2 console does not support custom vocabularies as it uses 16 kHz audio input.

Amazon Lex V2 uses custom vocabularies to elicit both intents and slots. The same custom vocabulary file is used for intents and slots. You can selectively turn off the custom vocabulary capability for a slot when you add a slot type.

Eliciting an intent – You can create a custom vocabulary for eliciting an intent. These phrases are used to transcription when your bot is determining the user's intent. For example, if you configured the phrase "backup" in your custom vocabulary, Amazon Lex V2 transcribes the user input to "can you please backup my photos?"—even when the audio sounds like "can you please pack up my photos." You can specify the degree of boosting for each phrase by configuring a weight of 0, 1, 2, or 3. You can also specify an alternate representation for the phrase in the final speech to text output by adding a displayAs field.

The custom vocabulary phrases used for improving transcription during intent elicitation don't affect transcriptions while eliciting slots. For more information about creating a custom vocabulary for eliciting intents, see Creating a custom vocabulary for eliciting intents and slots.

Eliciting custom slots – You can use a custom vocabulary to improve slot recognition for audio conversations. To improve your Amazon Lex V2 bot's ability to recognize slot values, create a custom slot and add the slot values to the custom slot, then choose Use slot values as custom vocabulary. Examples of slot values include product names, catalogs, or proper nouns. You shouldn't use common words or phrases such as "yes" and "no" in custom vocabularies.

After the slot values are added, these values are used for improving slot recognition when the bot is expecting input for the custom slot. These values aren't used for transcription when eliciting an intent. For more information, see Adding slot types.

Best practices for creating a custom vocabulary

Eliciting an intent

  • Custom vocabularies work best when used to target specific words or phrases. Only add words to a custom vocabulary if they are not readily recognized by Amazon Lex V2.

  • Decide how much weight to give a word based on how often the word isn't recognized in the transcription and how rare the word is in the input. Difficult to pronounce words require a higher weight.

  • Use a representative test set to determine if a weight is appropriate. You can collect an audio test set by turning on audio logging in conversation logs.

  • Avoid using short words like "on," "it," "to," "yes," "no" in a custom vocabulary.

Eliciting a custom slot

  • Add the values to the custom slot type that you expect to be recognized. Add all the possible slot values for the custom slot type, no matter how common or rare the slot value is.

  • Enable the option only when the custom slot type contains a list of catalog values or entities such as product names or mutual funds.

  • Disable the option if the slot type is used to capture generic phrases such as "yes," "no," "I don't know," "maybe," or generic words such as "one," "two," "three."

  • Limit the number of slot values and synonyms to 500 or less for best performance.

Enter acronyms or other words whose letters should be pronounced individually as single letters separated by a period and a space. Don't use individual letters unless they are part of a phrase, such as "J. P. Morgan" or "A. W. S." You can use upper- or lower-case letters to define an acronym.

Creating a custom vocabulary for eliciting intents and slots

You can use the Amazon Lex V2 console to create and manage a custom vocabulary, or you can use Amazon Lex V2 API operations. There are 2 ways of creating a custom vocabulary through the console:

Import custom vocabulary in the console:

  1. Open the Amazon Lex V2 console at https://console.aws.amazon.com/lexv2/home

  2. From the list of bots, choose the bot which you want to add the custom vocabulary.

  3. On the bot detail page, from the Add languages section, choose View languages.

  4. From the list of languages, choose the language to which you want to add the custom vocabulary.

Create a new custom vocabulary directly through the console:

  1. Click on Create in the Custom Vocabulary section of the language details page. This will open an editing window with no custom vocabulary present.

  2. Add inputs for phrase, DisplayAs, and weight as required. You can further make inline edits to added items by updating their fields or deleting them from the list.

  3. Click on Save. Please note: the new custom vocabulary is only saved in your bot after you click on Save.

  4. You can continue making inline edits in this page and click Save when are done.

  5. This page also allows you import, export, and delete a custom vocabulary file from the drop-down menu on the top right.

Use the ListCustomVocabularyItems API to view the custom vocabulary entries:

  1. Use the ListCustomVocabularyItems operation to view the custom vocabulary entries. The request body will look like this:

    { "maxResults": number, "nextToken": "string" }
  2. Please note that maxResults and nextToken are optional fields for the request body.

  3. The response from the ListCustomVocabularyItems operation looks like this:

    { "botId": "string", "botVersion": "string", "localeId": "string", "customVocabularyItems": [ { "itemId": "string", "phrase": "string", "weight": number, "displayAs": "string" } ] }

Use the BatchCreateCustomVocabularyItem API to create new custom vocabulary entries:

  1. If your bot’s locale does not have a custom vocabulary created yet, please follow the steps to use the StartImport to create a custom vocabulary.

  2. After the custom vocabulary has been created, use the BatchCreateCustomVocabularyItem operation to create new custom vocabulary entries. The request body will look like this:

    { "customVocabularyItemList": [ { "phrase": "string", "weight": number, "displayAs": "string" } ] }
  3. Please note that weight and displayAs are optional fields for the request body.

  4. The response from the BatchCreateCustomVocabularyItem will look like this:

    { "botId": "string", "botVersion": "string", "localeId": "string", "errors": [ { "itemId": "string", "errorMessage": "string", "errorCode": "string" } ], "resources": [ { "itemId": "string", "phrase": "string", "weight": number, "displayAs": "string" } ] }
  5. As this is a batch operation, the request will not fail if one of the items fails to create. The errors list will contain information about why the operation failed for that specific entry. The resources list will contain all of the entries that were successfully created.

  6. For BatchCreateCustomVocabularyItem, you can expect see these types of errors:

    • RESOURCE_DOES_NOT_EXIST: The custom vocabulary does not exist. Follow the steps for creating a custom vocabulary before calling this operation.

    • DUPLICATE_INPUT: The list of inputs contains duplicate phrases.

    • RESOURCE_ALREADY_EXISTS: The given phrase for the entry already exists in your custom vocabulary.

    • INTERNAL_SERVER_FAILURE: There was an error in the backend while processing your request. This may indicate a service outage or another issue.

Use the BatchDeleteCustomVocabularyItem API to delete existing custom vocabulary entries:

  1. If your bot’s locale does not have a custom vocabulary created yet, please follow the steps for Use the StartImport to create a custom vocabulary to create one.

  2. After the custom vocabulary has been created, use the BatchDeleteCustomVocabularyItem operation to delete existing custom vocabulary entries. The request body will look like this:

    { "customVocabularyItemList": [ { "itemId": "string" } ] }
  3. The response from the BatchDeleteCustomVocabularyItem will look like this:

    { "botId": "string", "botVersion": "string", "localeId": "string", "errors": [ { "itemId": "string", "errorMessage": "string", "errorCode": "string" } ], "resources": [ { "itemId": "string", "phrase": "string", "weight": number, "displayAs": "string" } ] }
  4. As this is a batch operation, the request will not fail if one of the items fails to delete. The errors list will contain information about why the operation failed for that specific entry. The resources list will contain all of the entries that were successfully deleted.

  5. For BatchDeleteCustomVocabularyItem, you can expect see these types of errors:

    • RESOURCE_DOES_NOT_EXIST: The custom vocabulary entry you are trying to delete does not exist.

    • INTERNAL_SERVER_FAILURE: There was an error in the backend while processing your request. This may indicate a service outage or another issue.

Use the BatchUpdateCustomVocabularyItem API to update existing custom vocabulary entries:

  1. If your bot’s locale does not have a custom vocabulary created yet, please follow the steps for Use the StartImport to create a custom vocabulary to create a custom vocabulary.

  2. After the custom vocabulary has been created, use the BatchUpdateCustomVocabularyItem operation to update existing custom vocabulary entries. The request body will look like this:

    { "customVocabularyItemList": [ { "itemId": "string", "phrase": "string", "weight": number, "displayAs": "string" } ] }
  3. Please note that weight and displayAs are optional fields for the request body.

  4. The response from the BatchUpdateCustomVocabularyItem will look like this:

    { "botId": "string", "botVersion": "string", "localeId": "string", "errors": [ { "itemId": "string", "errorMessage": "string", "errorCode": "string" } ], "resources": [ { "itemId": "string", "phrase": "string", "weight": number, "displayAs": "string" } ] }
  5. As this is a batch operation, the request will not fail if one of the items fails to delete. The errors list will contain information about why the operation failed for that specific entry. The resources list will contain all of the entries that were successfully updated.

  6. For BatchUpdateCustomVocabularyItem, you can expect see these types of errors:

    • RESOURCE_DOES_NOT_EXIST: The custom vocabulary entry you are trying to update does not exist.

    • DUPLICATE_INPUT: The list of inputs contains duplicate itemIds.

    • RESOURCE_ALREADY_EXISTS: The given phrase for the entry already exists in your custom vocabulary.

    • INTERNAL_SERVER_FAILURE: There was an error in the backend while processing your request. This may indicate a service outage or another issue.

Creating a custom vocabulary file

A custom vocabulary file is a tab-separated list of values that contain the phrase to recognize, a weight to give the boost, and a displayAs field which will replace the phrase in the speech transcript. Phrases with a higher boost value are more likely to be used when they appear in the audio input.

The custom vocabulary file must be named CustomVocabulary.tsv, and must be compressed in a zip file before it can be imported. The zip file must be less than 300 MB in size. The maximum number of phrases in a custom vocabulary is 500.

  • phrase 1–4 words that should be recognized. Separate words in the phrase with spaces. You can't have duplicate phrases in the file. The phrase field is required.

  • weight – The degree to which the phrase recognition is boosted. The value is an integer 0, 1, 2, or 3. If you don't specify a weight, the default value is 1. Decide on the weight based on how often the word isn't recognized in the transcription and on how rare the word is in the input. The weight 0 means that no boosting will be applied and the entry will only be used for performing replacements using the displayAs field.

  • displayAs – Defines how you want your phrase to look in your transcription output. This is an optional field in the custom vocabulary.

The custom vocabulary file must contain a header row with the headers "phrase," "weight," and "displayAs". The headers can be in any order, but must follow the above nomenclature.

The following example is a custom vocabulary file. The required tab character to separate the phrase, the weight, and the displayAs is represented by the text "[TAB]". If you use this example, replace the text with a tab character.

phrase[TAB]weight[TAB]displayAs Newcastle[TAB]2 Hobart[TAB]2[TAB]Hobart, Australia U. Dub[TAB]1[TAB]University of Washington, Seattle W. S. U.[TAB]3 Issaquah Kennewick