Standard Syntactic Metalanguage

In the rest of this chapter, we shall be describing the syntax of the configuration language. To make sure that this description is precise and unambiguous, we shall make use of a metalanguage, that is, a language specifically designed for describing other languages.

The metalanguage we shall use is the one specified by British Standard 6154. Many readers will be familiar with similar metalanguages, particularly those of the well-known Backus-Naur family, so here we shall give only a brief description of BS6154. For more detail, you should consult the standard itself. There is also a tutorial introduction, which is available from the National Physical Laboratory in England.

•	Terminal strings of the language—those not built up by rules of the language—are enclosed in quotation marks.

•	Non-terminal phrases are identified by names, which may consist of several words separated by spaces.

•	A sequence of items may be built up by connecting them with commas.

•	Vertical bars (\|) separate alternatives.

•	Optional sequences are enclosed in square brackets ([ and ]).

•	Sequences that may be repeated zero or more times are enclosed in braces ({ and }).

•	Each phrase definition is built up using an equals sign to separate the two sides, and a semi-colon to terminate the right hand side.