Concrete syntax and exchange format are described in section 6.
It acts as a pivot between the concrete syntax description and the semantics description.
Some DSL developers consider that in modern visual (or graphical) language environments there is no need to be very specific about concrete syntax.
It is clear that a mapping from abstract syntax to a concrete syntax is as important as the inverse mapping.
For simple languages and in most of the current DSM tools, concrete syntax representation is directly mapped to the abstract syntax.