DDIO is a VSAM file where Xpediter saves the listing of the source-code. During compilation (or as a separate job) you can add a step to insert the compiler's output (aka listing) into the specified DDIO file.
During debug, Xpediter uses the DDIO to to show the listing of the traced code.
DDIO File ===> Required. Specify a DDIO File or use DDIOCre command if one has not already been created. Statistical information
about a program is written to this file during compile time which in turn is later used when in a debug session.