Attempto Controlled English (ACE) is a controlled natural language specifically designed for requirements specifications and knowledge representation. ACE is a subset of English with a restricted grammar constrained by a small set of construction and interpretation rules.
In this report, we describe the syntax of ACE, version 4.0, and present an abstract grammar for it in the form of phrase structure rules enhanced by features. The report aims at the implementer who is interested in the linguistic background of ACE. It underlies the current version of the Attempto parser. It is not intended to be a reference manual for the user of ACE.