FAQs(1 to 15)

1)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.

2)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.

3)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.

4)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.

5)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.

6)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.

7)How is a dataset passed fromone 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.

8)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:




9)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.

10)Name some ofthe JCL statements that are not allowed in procs.?

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

1. JOB, Delimiter(/*), or Null statements

2. JOBLIB or JOBCAT DD statements

3. DD * or DATA statements

4. Any JES2 or JES3 control statements

11)What is primary allocation for a dataset?

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

12)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.

13)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.

14)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.

15)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.