  What is here called controlled natural language (CNL) has traditionally been
given many different names. Especially during the last four decades, a wide
variety of such languages have been designed. They are applied to improve
communication among humans, to improve translation, or to provide natural and
intuitive representations for formal notations. Despite the apparent
differences, it seems sensible to put all these languages under the same
umbrella. To bring order to the variety of languages, a general classification
scheme is presented here. A comprehensive survey of existing English-based CNLs
is given, listing and describing 100 languages from 1930 until today.
Classification of these languages reveals that they form a single scattered
cloud filling the conceptual space between natural languages such as English on
the one end and formal languages such as propositional logic on the other. The
goal of this article is to provide a common terminology and a common model for
CNL, to contribute to the understanding of their general nature, to provide a
starting point for researchers interested in the area, and to help developers
to make design decisions.
