JCL-6

Q)      What is a Generation Data Group (GDG)?

A)      Generation Data Group is a group of chronologically or functionally related datasets. GDGs are processed periodically, often by adding a new generation, retaining previous generations, and sometimes discarding the oldest generation.

Q)      How is a GDG base created?

A)       A GDG base is created in the system catalog and keeps track of the generation numbers used for datasets in the group. IDCAMS utility is used to define the GDG base.

Q)      What is model dataset label(Model DSCB)?

A)       A model dataset label is a pattern for the dataset label created for any dataset named as a part of the GDG group. The system needs an existing dataset to serve as a model to supply the DCB parameters for the generation data group one wishes to create. The model dataset label must be cataloged. The model DSCB name is placed on the DCB parameter on the DD statement that creates the generation data group.

Q)      How are GDGs concatenated?

A)       Generation Data  Groups are concatenated by specifying each dataset name and the generation number for all generations of the generation data group.  Otherwise to have all generations of a generation data group, omit the generation number. The DD statement will refer to all generations. The result is the same as if all individual datasets were concatenated. If generations are not on the same volume, this will not work.

Q)      How is a new GDG coded?

A)       A new GDG is coded as (+1) after the dataset name as follows: DSN=JAN.DATA(+1). This will cause all generations to be pushed down one level at the end of the job.

Q)      When should DISP=MOD is used?

A)       DISP=MOD is used to either extend an existing sequential dataset or to create a dataset if it does not exist. If the dataset exists, then records are appended to the dataset at the end of the existing dataset. If the dataset does not exist, the system treats MOD as if it were NEW, provided that the volume parameter has not been used. If the volume parameter is used, the system terminates the job and does not create the new dataset. MOD can be used to add to a dataset that extends onto several volumes. Always specify a disposition of CATLG with MOD for cataloged datasets, even if they are already cataloged, so that any additional volume serial numbers will be recorded in the catalog.

Q)      How is a dataset passed from  one step to another?

A)       A dataset is passed from one step to another based on what is coded on the DISP parameter. The dataset can only be passed to subsequent steps if PASS was used on the disposition parameter.

Q)      How are datasets concatenated?

A)       Datasets are concatenated by writing a normal DD statement for the first dataset and then adding a DD statement without a DDNAME for each dataset to be concatenated in the order they are to be read. The following is an example of three datasets concatenated:

//YEARDAT            DD      DSN=JAN.DATA,DISP=SHR

//                   DD      DSN=FEB.DATA,DISP=SHR

//                   DD      DSN=MAR.DATA,DISP=SHR

Q)      What is the difference between the JOBLIB and the STEPLIB statements?

A)   The JOBLIB statement is placed after the JOB statement and is effective for all job steps. It cannot be placed in a

         cataloged procedure. The STEPLIB statement is placed after the EXEC statement and is effective for that job step

         only. Unlike the JOBLIB statement, the STEPLIB can be placed in a cataloged procedure.

Q)  Name some of  the JCL statements that are not allowed in procs.?

A) Some of the JCL statements which are not allowed in procedures are:

JOB, Delimiter(/*), or Null statements

2. JOBLIB or JOBCAT DD  statements

3. DD * or DATA statements

4. Any JES2 or JES3 control statements

Q)  What is primary allocation for a dataset?

A)  The space allocated when the dataset is first created.

Q)  What is the difference between primary and secondary allocations for a dataset?

A)  Secondary allocation is done when more space is required than what has already been allocated.

Q)  How many extents are possible for a sequential file ? For a VSAM file ?

A)        16 extents on a volume for a sequential file and 123 for a VSAM file.

Q)  What does a disposition of (NEW,CATLG,DELETE) mean? 

A)        That this is a new dataset and needs to be allocated,  to CATLG the dataset if the step is successful and to delete the dataset if the step abends.

Q)  What does a disposition of (NEW,CATLG,KEEP) mean?

A)        That this is  a new dataset and needs to be allocated, to CATLG the dataset if the step is successful and to KEEP but not CATLG the dataset if the step abends. Thus if the step abends, the dataset would not be catalogued and we would need to supply the vol. ser the next time we refer to it.

Q)  How do you access a file that had a disposition of KEEP? 

A)        Need to supply Volume Serial  Number VOL=SER=xxxx. 

Q)  MOD, DELETE;  What does a disposition of (,DELETE) mean ?

A)        The MOD will cause the dataset to be created (if it does not exist),  and then the two DELETEs will cause the dataset to be deleted whether the step abends or not. This disposition is used to clear out a dataset at the beginning of a job.

Q)  What is the DD statement for a output file?

A)        Unless allocated earlier, will have the following parameters:  DISP=(NEW,CATLG,DELETE), UNIT , SPACE & DCB

Q)  What do you do if you do not want to keep all the space allocated to a dataset?

A)        Specify the parameter  RLSE ( release ) in the SPACE e.g. SPACE=(CYL,(50,50),RLSE)

Q)  What is DISP= (NEW,PASS,DELETE)?

A)        This is a new file and create it, if the step terminates normally, pass it to the subsequent steps and if step abends, delete it.  This dataset will not exist beyond the JCL.

Q)  How do you create a temporary dataset?  Where will you use them?

A)        Temporary datasets can be created either by not specifying any DSNAME or by specifying the temporary file indicator as in DSN=&&TEMP. We use them to carry the output of one step to another step in the same job. The dataset will not be retained once the job completes.

Q)  How do you restart a PROC from a particular step?

A)        In job card, specify RESTART=PROCSTEP.STEPNAME where PROCSTEP = name of the JCL step that invoked the PROC and STEPNAME = name of the PROC step where you want execution to start

Q)  How do you skip a particular step in a proc/JOB? 

A)        Can use either condition codes or use the jcl control statement IF (only in ESA JCL).

Q)  A PROC has five steps.  Step 3 has a condition code.  How can you override/nullify this condition code? 

A)        Provide the override on the EXEC stmt in the JCL as follows:

//STEP001 EXEC procname, COND.stepname=value

All parameters on an EXEC stmt in the proc such as COND, PARM have to be overridden like this.

Q)  How do you override a specific DDNAME/SYSIN in PROC from a JCL?

A)        //<STEPNAME.DD>    DSN=...

Q)  What is NOTCAT 2?

A)        This is an MVS message indicating that a duplicate catalog entry exists. E.g., if you already have a dataset with dsn = 'xxxx.yyyy' and u try to create one with disp new, catlg, you would get this error. the program open and write would go through and at the end of the step the system would try to put it in the system catalog. at this point since an entry already exists the catlg would fail and give this message. you can fix the problem by deleting/uncataloging the first data set and going to the volume where the new dataset exists(this info is in the msglog of the job) and cataloging it.

Q)  What is 'S0C7' abend?

A)        Caused by invalid data in a numeric field.

Q)  What is a S0C4 error ?

A)        Storage violation error - can be due to various reasons. e.g.: READING a file that is not open, invalid address referenced due to subscript error.