You can use a SAS fileref or the ddname as a convenient
way of referring to a VSAM data set in a SAS language statement or
command. The first time the ddname is used in a SAS statement or procedure,
SAS assigns it as a fileref for the VSAM data set. Alternatively,
you can use the FILENAME statement to associate a fileref with a VSAM
data set. The FILE statement later uses the fileref rather than the
data set name to refer to the data set.