What is a GDG? How is it referenced? How is it defined? What is a MODELDSCB? GDG stands for generation data group. It is a dataset with versions that can be referenced absolutely or relatively. It is defined by an IDCAMS define generation datagroup execution.

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Sunitha

  • Jun 29th, 2005
 

Hi, How will you refer the same GDG version in different JCL's? Can u pls tell me how will we code that?

nhenshall

  • Sep 11th, 2005
 

It is defined using an IDCAMS command DEFINE GENERATIONDATAGROUP or DEF GDG for short. Not many parameters, just a maxgeneration as I recall.

If you create a GDG called MY.GDG, this first instance will be cataloged as MY.GDG.G00001V00 and onwards. Each time you reference one you can do so by absolute reference, as above, or relative. MY.GDG(0) which is the most recent generation. MY.GDG(-1) is the next oldest, and so on.

To create a new GDG generation, you code in your JCL ..DSN=MY.GDG(+1), DISP=(NEW,CATLG) etc as normal. Whatever you created as a max generations, the last one gets dropped off (uncataloged and deleted) assuming you have that many generations.

They are useful for backups and the like. If you run a particular batch job on a daily basis, then its often the case that you have a 5 generation (or 7?!) GDG to capture your output or parameters etc. You then have a week to print them or reference them.

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Bibhu

  • Mar 31st, 2006
 

Model DCB is used because to avoid writting the characterstics of the generations repeatedly. The advantage is that we assign the characterstic of a dataset to all the generations by specifying the model DCB.There is a less chance of getting error.

Note: All the generations of a GDG should have the same characterstics.

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Any new GDG in a job is defined as +1. Other steps in the same job will refer to it as +1. However if the job abends after the allocation step, you can restart the job, but must change the +1 to 0 in the remaining steps.Of course, nearly every scheduling & restart system will take care of this for you.

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sanjay

  • Jun 11th, 2007
 

gdg is a group data set which are related to each other pronounly & functionaly
it smiliar to array which store many type of group data'sets
 

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nthayyuru

  • Mar 30th, 2009
 

GDG nothing but Generation Data Group, means data sets has been generated with version number.

It will be referred as a dataset with version number then only we knows and identifying the dataset when it was created and easily identifying the data is stored in the dataset with help of version number.

BY using the IDCAMS utility we can define the GDG. Before that we can create the GDG base.

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GDG is a Generation Data Group which is having grouped related datasets chronologically or functionally. It is referenced with the versions those are absolute and relative. It is defined by idcams generation data group execution. A model dscb is nothing but the system needs dcb parameters for every data set to create generations for GDG.

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