abstract syntax
     
         A representation of data (typically either a
        message passing over a communications link or a program being
        compiled) which is independent of machine-oriented structures
        and encodings and also of the physical representation of the
        data (called "concrete syntax" in the case of compilation or
        "transfer syntax" in communications).
     
        A compiler's internal representation of a program will
        typically be specified by an abstract syntax in terms of
        categories such as "statement", "expression" and "identifier".
        This is independent of the source syntax (concrete syntax)
        of the language being compiled (though it will often be very
        similar).  A parse tree is similar to an abstract syntax
        tree but it will typically also contain features such as
        parentheses which are syntactically significant but which are
        implicit in the structure of the abstract syntax tree.
     
        (1998-05-26)