Controlled English as a Way of Standardizing Content

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June 2000

Controlled English as a Way of Standardizing Content

CIDMIconNewsletter Katherine Brennan Murphy, Center Associate

In this issue’s feature article, Ginny Redish discusses ways of structuring documents to facilitate single sourcing. Organizations who employ a Controlled English standard also reap benefits when moving to single sourcing. This case study offers success stories from Caterpillar Tractor and Boeing and the lessons we learned at Tektronix when we proposed developing work instructions using Controlled English.


After World War II, manufacturers of large equipment found that they needed to provide maintenance manuals to service centers in countries where English was not the primary language. For the Caterpillar company, the equipment they produce is often still found working in almost any country in the world 50 years after it was built.

As for Boeing, airplanes must be serviced at specific intervals to meet certification requirements. At least half of the maintenance personnel who work for airlines around the world do not read English. Maintenance manuals for airplanes are many thousands of pages long. By international agreement, translation into other languages is not required, so Boeing writes the maintenance manuals in English. In fact, if aerospace manufacturers translate the manuals, they are liable for the accuracy of the translations. In the aerospace industry, mistakes caused by faulty translations can be life threatening.

With the Esperanto movement as a precedent, linguists and writers began considering the idea that perhaps a subset of English could be developed and then taught to maintenance personnel around the world. This subset would have strict grammar rules and a very carefully controlled vocabulary. Out of these early attempts, Controlled English language standards have developed.


Caterpillar Tractor Corporation was one of the earliest corporations to develop and teach a form of Controlled English, called Caterpillar Fundamental English. They wrote documents in Caterpillar Fundamental English and taught non-English readers at their regional service centers how to read and comprehend this form of English. It took 1 to 1H years for the technicians to be trained, and Caterpillar often had to find people who were willing to go to remote areas as trainers.

However, with a stable, well-paid workforce, this process met the needs of maintenance in areas where the Roman character set is used. As Caterpillar expanded its global market, several problems arose. Often the people being trained were not Caterpillar employees, and once they learned some English, they left for other jobs. Also, it was harder to find people willing to go to remote or dangerous areas to train others. Finally, when working in cultures whose native character set was other than Roman, Caterpillar first had to teach an entirely new alphabet as well as a new language.

Over time, the investment, both in writing and teaching, became too costly to maintain. Caterpillar created writing guidelines for all English manuals to facilitate translation and relied on the competence and diligence of its writers and editors to use standard grammar and vocabulary. Given the enormous number of pages produced and the fact that engineers wrote the procedures, this ad hoc process broke down over time. The final demise of Caterpillar Fundamental English was the rapidly increasing complexity of the equipment, especially the electronics and advanced engine controls. The extremely small and simple vocabulary was clearly insufficient.

In the mid 1980s, Caterpillar began automating the documentation process, moving the documents onto computers and beginning to look at machine translation. However, efficient and accurate machine translation requires that the input vocabulary and sentence structure be unambiguous. This requirement can be difficult to achieve when more than 180 authors are contributing to the manuals.

Caterpillar also began planning to create documents using information elements so that text could be stored, reused, and modified in one place. To meet these requirements, they worked with the Language Technologies Institute (LTI) at Carnegie Mellon University to develop an authoring tool that assists authors to follow the writing guidelines and use standardized vocabulary. This tool internally diagrams each sentence the author writes and provides information on how the sentence may not meet the standards. This tool has made four contributions to the authoring process:

  • Provides authors with immediate feedback on documents as they write, which allows the tool to be, in effect, a training aid
  • Creates a process to maintain a standard vocabulary, while adding and deleting words, which facilitates machine translation
  • Enables the single-sourcing process
  • Improves productivity and accuracy through text reuse

Eric J. Adolphson manages the group at Caterpillar that maintains the language integrity of this system. Adolphson has completed advanced post-graduate work in Computational Linguistics and, with two other writing professionals, specifies to the authoring system how to apply the rules. This group also screens requests from authors to add new words to the master dictionary. Each word must have a clear definition that removes ambiguity. Over 1,000,000 words are processed by the authoring system each week. Of these, 60 new terms are added to the dictionary. Caterpillar’s maintenance systems are highly automated, allowing the day-to-day maintenance of a complex, controlled-language application to be performed by three people. Development of the system and the machine translation components is performed at LTI.

At Caterpillar, authors have engineering backgrounds; they are hired primarily for their technical expertise rather than their writing skills. The authoring system helps create unified documentation that can be easily translated into native languages. Because Adolphson’s staff is available for consultation, the rules and vocabulary do not stagnate. The authors do sometimes chafe at the restrictions, saying “That’s what they call it in the field.” or “That’s what the engineers call it.” However, the system does ensure that these 180 writers consistently follow rules and use the same terminology throughout.

Adolphson also points out that standardization results in documents without much tone, especially in English because English has the largest vocabulary of any language. The repetitive vocabulary combined with a standard sentence style makes for bland sounding prose, which is not inappropriate for technical documentation. He also says that, sadly, authoring tools are replacing human editing. However, by following the guidelines and using the authoring tool’s suggestions, technical writers can learn to be better at their craft. For example, the authoring tool requires that no noun phrase be longer than three words unless it is the name of a part. Recasting these noun stacks requires considerable skill on the writer’s part.


The aircraft industry’s experience is similar to Caterpillar’s. Their motivation, though, was to fulfill stated customers’ needs. At least half of the maintenance workers of airline companies do not have English as their native language. The airlines they work for demand maintenance manuals that their employees can easily comprehend.

Fokker Aircraft began the Simplified English movement in the aircraft industry in the 1970s. In 1982, the Association Eurpeene des Constructeurs de Materiel Aerospatial (AECMA) and the Aerospace Industries Association (AIA), following Fokker’s lead, jointly developed an international standard that aircraft manufacturers and airline companies could use as a baseline (Gingras 1987, 25). The AECMA Simplified English standard, released in 1986, outlines style and grammar rules and lists both allowed and proscribed vocabulary. Boeing, in cooperation with 17 other companies, worked to create the standard. (See the summary of the AECMA standard on page 52.)

Boeing found the same issues as Caterpillar did when implementing the standard in house-writing in Simplified English is extremely difficult without authoring support. Writing good Simplified English requires a massive learning curve; most of the writers are engineers who are hired for their technical competence not just their writing skills. They need to be domain specialists.

Boeing’s Natural Language Processing group, managed by Jim Hoard, developed an authoring support tool called the Boeing Simplified English Checker. In production use since 1990, the checker is still maintained by the Natural Language Processing group. Jim has a PhD in Linguistics and many years of experience with Boeing. His staff includes both linguists and computer scientists. Over 1,000 authors use this tool.

The Boeing Simplified English Checker runs on top of authoring tools (including Adept and Microsoft Word). There is also a Web-based interface. The authors submit their text to the checker, and they receive feedback on violations of the Simplified English writing rules and vocabulary restrictions.

Authors attend a short class where they learn about the philosophy and goals of Simplified English. All of their training comes from using the tool. There is still a steep learning curve, but it is lessened by using a convenient, interactive authoring tool.

Even though Boeing implemented this solution in response to customer needs, they have reaped additional internal benefits. First, they were able to gain consensus across product lines on technical terms. Second, their document management system uses the information elements to assemble manuals that are customized to a particular airline customer. Third, when the need arises for documents to be translated (for example, internal procedures at Boeing or marketing materials), the controlled vocabulary facilitates this process. Fourth, they have been able to turn this effort into a saleable product.


One of my professors in graduate school, Dr. Jan Spyridakis, had worked with Boeing on evaluating the comprehension of Simplified English texts. When I was faced with the task of trying to upgrade over 3,000 work instruction documents at Tektronix, I remembered the research Spyridakis had done. After looking through articles and talking with several contacts, I proposed that we consider implementing a variation of Simplified English for our process documents. To be usable, the system needed to accommodate the following parameters:

  • A stable workforce, a significant percentage of whom read English as a second language
  • An extensive work instruction library (more than 3,000) documenting 1,700 products with 8,000 options, with each document being revised (on average) every two months
  • A move to a more highly automated and customized manufacturing environment
  • A quality system that required manufacturing engineers to author work instructions< /li>
  • A move to online work instructions

We started our investigation by purchasing the AECMA standard and working on a vocabulary that was suitable for our manufacturing domain. I taught a four-week class for Manufacturing Engineers to give them an idea of what would be involved in such a process. My team also created some prototype online work instructions using Simplified English guidelines.

I left Tektronix not long after this project moved into the feasibility stage. However, the first order of business was to purchase authoring software or build it in house. We considered the software to be the most important ingredient because, as at Caterpillar and Boeing, our authors were engineers.

Ultimately, Tektronix decided not to pursue a Controlled English option. First, Tektronix went through a significant restructuring in 1999 and, as a result, did not have the resources to work on this project. Second, after I left, there were no information developers working in Manufacturing. Third, the Manufacturing Engineers decided that the rules and vocabulary would be too confining. Fourth, the system they had in place was adequate for now.


The experience of Caterpillar and Boeing shows that producing documents that conform to a Controlled English standard has definite benefits-both to the company and to the end users. Both Caterpillar English and Boeing Simplified English resulted in higher quality documents and lower costs to translate technical manuals. However, their experience, particularly Caterpillar’s, points out that without the authoring support tools, the cost is too high. This authoring support solves both the consistency and training problems that organizations can encounter when implementing such a system.

When supported by an interactive tool, technical authors can focus on content issues rather than style and word choice. In both of these successful implementations, there were overwhelming customer or internal requirements driving the move to Controlled English. My experience at Tektronix points out that without an overwhelming corporate need-translation, single sourcing, regulator requirements, customer needs, or tens of thousands of pages-the move to a Controlled English standard may be difficult to accomplish. This experience also reminds us of the importance of involving a consistent, strategic leader who can manage up and sideways as needed. Both Eric Adolphson and Jim Hoard provide this strategic leadership in their companies. If you are interested in learning more about their success stories or how you could apply their experience to your problems, please send them email. CIDMIconNewsletter