What is the meaning of data definition name (ddname) and dataset name (dsname) in the DD statement?

Data definition name is the eight character designation after the // of the DD statement. It matches the internal name specified in the steps executing program. In COBOL that's the name specified after the ASSIGN in the SELECT ASSIGN statement. Dataset name is the operating system (MVS) name for the file.

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Soumik Das

  • Feb 20th, 2007
 


The DD name is the logical 8 characters file name which alllows the pplication program to identify or tag the dataset.

Whereas the DSN is the physical file name used by the MVS to identify the dataset.

like in any application program we can write ...

in COBOL...
SELECT FILE ....ASSIGN TO IOFILE...

in PL/I

DCL IOFILE FILE RECORD OUTPUT ENV(FB RECSIZE(136));

here IOFILE is logical DD name......so during running the appliocation we need to code in the JCL....

//PLI.SYSIN  DD *
//IOFILE DD DSN=TEST.SAMPLE.DATA, DISP=SHR

here the DSN is the TEST.SAMPLE.DATA but the application program always identifies it by the DD name rather than the DSN.

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DD (or Data Definition) is an arbitrary 8 character file name that a program performs I/O to/from.
This directly correlates to to the DD name as specified in your JCL.  If these two 8 character DD names don't match, your program won't be able to communicate with any datasets. 
There can be, but doesn't HAVE to be a correlation between the dataset name.

Usually, when choosing a dd name, it's traditional to pick some sort of descriptor for the data that uses it.  The dsn attached to the name usually expounds on this ddname as well as its frequency of usage.

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