A Abstract Syntax

[CHANGED:] [] The abstract syntax is central to the definition of a formal language. It stands between the concrete representations of documents, such as marks on paper or images on screens, and the abstract entities, semantic relations, and semantic functions used for defining their meaning.

The abstract syntax has the following objectives:

• to identify and separately name the abstract syntactic entities;
• to simplify and unify underlying concepts, putting like things with like, and reducing unnecessary duplication.

The abstract syntax is presented as a set of production rules in which each sort of entity is defined in terms of its subsorts:

      SOME-SORT       ::=  SUBSORT-1  |  ...  |  SUBSORT-n

      SOME-CONSTRUCT  ::=  some-construct COMPONENT-1 ... COMPONENT-n

The context conditions for well-formedness of specifications are not determined by the grammar (these are considered as part of semantics).

The grammar here has the property that there is a sort for each construct (although an exception is made for constant constructs with no components). Appendix B provides an abbreviated grammar defining the same abstract syntax. It was obtained by eliminating each sort that corresponds to a single construct, when this sort occurs only once as a subsort of another sort.

The following nonterminal symbols correspond to lexical syntax, and are left unspecified in the abstract syntax: WORDS, SIGNS, DOT-WORDS, PLACE, URL, PATH, and NUMBER.