8.2 Unit Specifications

      UNIT-SPEC-DEFN   ::= unit-spec-defn SPEC-NAME UNIT-SPEC
      UNIT-SPEC        ::= UNIT-TYPE | SPEC-NAME | ARCH-UNIT-SPEC
                         | CLOSED-UNIT-SPEC

A unit specification definition UNIT-SPEC-DEFN is written:

unit spec

SN =

USP

end

It provides a name SN for a unit specification USP. The unit specification may be a unit type. It may also be the name of another unit specification (in the context-free concrete syntax, this is indistinguishable from a reference to a named structured specification in a constant unit type, but the global environment determines how the name should be interpreted). It may be an architectural specification (either a reference to the defined name of an architectural specification, or an anonymous architectural specification). Finally, it may be an explicitly-closed unit specification.

It defines the name SN to refer to the unit specification USP, extending the global environment (which must not already include a definition for SN). The local environment given to USP is empty, i.e., the unit specification is implicitly closed.