Controlled Languages and Speech Prompts

"Welcome to the Ajax speech application. It is possible to perform any of several actions at any time during this application, including the common actions of asking for help, transferring the call to an operator, stopping the application and returning to the main menu."

The sample prompt above is too long and confusing for most users. However, by using a controlled language, you can improve the prompt for your customers.

What is a controlled language?

A controlled language is a sub-language of English, or other widely spoken language, with specific grammar, style and vocabulary rules. Many companies, industries, and governmental agencies design controlled languages for writing all types of public information, such as technical manuals and contracts. Controlled languages improve readability and comprehension by using:

  • Short sentences
  • Active verbs
  • Personal pronouns
  • A limited, approved vocabulary

    How long have controlled languages been used?

    Controlled languages have been used for decades. Linguists developed a "minimal" type of English called "Basic English" in the 1930s. In the 1960s, the Caterpillar Tractor Company developed "Caterpillar Fundamental English" for easily understood technical manuals.

    The most well-known model for many subsequent controlled languages is "Simplified English." The European Association of Aerospace Industries (AECMA) developed "Simplified English" in the late 1970s for all maintenance documentation.

    Other major controlled languages include the U.S. Government's "Plain Language," the United Kingdom's "Plain English," and the European Commission Translation Service's "Fight the Fog."

    How can controlled language help the speech world?

    In a sense, the world of speech already has one standard controlled language. The European Telecommunications Standards Institute (ETSI) standard of common commands in five languages—English, French, German, Italian and Spanish—is a controlled language for communication devices and services. The clear, concise commands are natural responses in each language. (For more information, see "Uniform Basic Function Commands," Speech Technology Magazine, January/February 2003 or go to the ETSI Web site at http://www.etsi.org.

    Speech applications will benefit by using controlled languages. Because of their simplified syntax and restricted vocabulary, controlled languages are more natural and easier to understand, especially when spoken by a text-to-speech synthesizer over a telephone. Non-native speakers will be able to understand the simple syntax and vocabulary with less training and experience with the natural language.

    A controlled language for speech applications should contain the following:

  • Simplified syntax. Use simple sentences rather than compound sentences or sentences with dependent clauses. Use active verbs for sentences rather than passive voice. Use personal pronouns such as "you" and "we."
  • Natural sounding language. "Voice user interfaces (VUIs) should use ordinary language, as it is spoken today." (See C. Henton and G. K. Pullum, "Whom Should I Say Is Calling? Prescriptive Grammar from a Hundred Years Ago Can Ruin a Good VUI," Speech Technology Magazine, November/December 2002.)
  • Human factors guidelines. Use short, concise and consistent prompts. Include possible answers in the prompts. (For additional human factors guidelines, see B. Balentine and D. P. Morgan, How to Build a Speech Recognition Application, Second Edition. EIG Press, 2002, pp. 33-70.)
  • Constrained vocabulary. Use the ETSI common commands for telephone control. Select and use a domain-specific vocabulary (see B. Balentine and D.P. Morgan, How to Build a Speech Recognition Application, Second Edition, EIG Press, 2002, pp. 71-96).

    Developers need tools for speech applications similar to grammar checkers in word processing applications. Controlled language checkers examine each prompt, verify that the prompt conforms to the controlled language and offer suggestions for revising prompts so they conform. Unfortunately, they do not apply human factors guidelines to speech applications. (See the sidebar for links to three vendors with controlled language checkers. With the use of controlled languages, developers can create speech applications with natural responses that are easy-to-learn and consistent. Until controlled language checkers are available as tools in speech application development toolkits, developers should apply controlled language principles to speech application prompts manually.

    When using controlled language principles, the sample prompt at the top of this column is easier to understand:

    "Welcome to the Ajax speech application. You can say 'help,' 'operator,' 'stop,' or 'main menu' at anytime during this call."

    Dr. James A. Larson is Manager of Advanced Human Input/Output at Intel, and author of the book, VoiceXML -- Introduction to Developing Speech Applications. He can be reached at jim@larson-tech.com and his Web site is http://www.larson-tech.com.
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