The name of a DD statement that identifies a PDSE data set, a concatenation of PDS and PDSE data sets, or a UNIX path. Note that fast data cannot process PDS members in a mixture of PDS and PDSE. Although a DD name is normally thought of as an 8-character field, it is treated here as a varying length character string beginning with a two-byte binary length field. The length is the number of bytes in the ddname, excluding the length field itself.