JCL- Characteristics of GDG

• All datasets within GDG share same name except the last qualifier which is made of generation number and version number
• Generation number is automatically assigned by Operating System
  Syntax:- GaaaaVxx
  Where,
  aaaa - absolute generation number, 0001 to 9999
  xx - version number, 00 to 99
  
• Datasets within GDG can be referenced by its relative generation number.
  • GDGBASENAME(0) references current generation
  • GDGBASENAME(-1) refers to generation just before the current generation
  • GDGBASENAME(+1)refers to the next generation data set just after the current one
• It can also be referenced by actual name of generation dataset for example:- ‘PAYROLL.SALARY.MONTHLY.G0001V00’
• Generations are updated only at the end of the job, meaning:-
  • JOB STEP1 creates one generation, code it as GDGBASENAME(+1)
  • JOB STEP2 creates one more generation, then you have to code it as GDGBASENAME(+2) because the (+1) is not yet promoted to current generation.
  • For any executing job the current generation remains same until it ends. So in above case GDGBASENAME(+2) will get promoted to current generation only after execution of job