GDG related doubt 1

[NewItron]

Hi,
Can anybody please tell me whats is the structure of a base GDG ? I have tried making different versions of different LREC manually by copying and changing the "Gnnn" of a prev generation.It works!! Why is it not possible to make a VSAM file as one of the generations of a GDG?
Regards
NewItron

 

[webrabbit]

A GDG is actually a catalog function. It is defined in the catalog and the catalog assigns the generation number to the name. The GDG definition is just an entry in the catalog. The entry is set up with IDCAMS, but the datasets must be allocated via JCL. Since all VSAM files must be allocated and cataloged with IDCAMS and not via the JCL, you cannot have a VSAM GDG. GDG's can be QSAM, BDAM, BSAM, or (if the os still supports it) ISAM.