An NDF data structure allows for the possibility of storing the values of its array components in a variety of different ways within the underlying data system HDS. The reasons for this are various, but have to do with maintaining compatibility with previous data formats and optimising disk space or access time for certain kinds of information. The options are described in SGP/38, where they correspond with the various variants of the ARRAY structure, which is one of the building-blocks from which an NDF is constructed.
In the present document, the terminology has been changed slightly.
In particular, the term storage form is used in preference to
variant to avoid possible confusion with variance,
although the meaning is unchanged.
NDF [1ex