How IMS knows what physical VSAM datasets to access

gautam79 · New User Joined: 30 Aug 2006 Posts: 11 Location: India

Hi,

An IMS application program uses PSB to access a database. PSB has DBD name and it comes to know what database to go and access.

What i want to know is how does IMS comes to know, which physical dataset corresponds to a particular database?

Please try to explain in detail!!
Thanks

Devzee · Posted: Sat Mar 10, 2007 1:36 am

We can tell the JOb to refer to Physical dataset by giving the corresponding DD name in the JCL.

//DBDNAME DD DSN=ACTUAL PHYSICAL Dataset

In some work sites there will be default physical dataset name allocation in that case you dont have to give the actual physical dataset name.
To use this default there should be some library like DYNALLIB in the JOBLIB statement of your job

gautam79 · New User Joined: 30 Aug 2006 Posts: 11 Location: India

Thanks devzee, but in our case, we were using those DD names for our old JCLs, but when new version of IMS was implemented, after that we didnt require to use those DD names. The IMS would resolve those on its own.

Someone actually told me that RESLIB actually takes care of these. is that true?

Devzee · Posted: Tue Mar 13, 2007 10:49 am

It really depends how your system and jcls are configured.

Actually RESLIB contains load modules for IMS, for DD names we use DYNALLIB in JOBLIB card.