IBM Mainframe Forum

Folks -

I am coding COBOL-IMS DBIO Programs to get my hands wet. The snapshot below, shows the DBD Database Structure of the IMS Database.

DBD Database Structure :



Data Stored :


Note : The Level of indentation corresponds to the level in the IMS-DB Hierarchical Structure. First level-of-indentation : VENDRSEG Segment, Second Level-of-Indentation : ITEMSSEG, Third Level-of-indentation : STLOCSEG

Problem : I have coded a COBOL Program that PERFORMs the Following Tasks :

1. 520-ESTABLISH-PARENTAGE at the VENDOR Segment, By Executing the following CALL


After the CALL was executed, the PCB Storage Area dump was,

PCB DUMP :


2. 550-GOTO-LAST-LOCATION traverses through the STOCK-LOCATION Segment Occurrences, UNTIL STATUS-CODE='GE'.


After the PERFORM Block was executed, the PCB Storage Area dump was,

PCB DUMP :


3. 570-RESET-POSITION SHOULD reset the Database Position, back to square one - the First STOCK LOCATION Segment Occurrence, by executing a GNP CALL, with Command-Code F.



After the GNP CALL with F Command-code was executed, the PCB Storage Area dump was,

PCB DUMP :


When I print the contents of the Segment IO-Area, it displays the INCORRECT Output.

The correct and expected Output after resetting the Database-Pointer to the FIRST Stock-Location under the established Parent, should be 'DEL 1500 300 450 160204'.


Attached herewith, please find 1) Program Source-Code 2) Compile-Listing with the expanded Copy-books and 3) Output-Listing obtained after running the Program. Kindly advise, as to what changes should I make, to get the Expected Result.

Thank you very much.

You have not reset parentage to ITEMSEG=11 so you are at ITEMSEG=12 and the first STLOCSEG here is for the segment returned.

Hi Nick -

I believe that would have been the case, if I had set the Parentage at ITEM SEGMENT Level. However, I am setting the Parentage at the VENDOR SEGMENT Level, and not the ITEM SEGMENT Level.

Here is the CALL, which establishes the Parentage once again -


Thanks and appreciate your help. Expecting your comments and thoughts on the same.

Hi Quasar,

I am not very much familiar with the IMS traversing but I agree with Nic. Though you established parentage initially but since you processed all the STLOCSEG segments under VENDRSEG using unqualified calls and STLOCSEG is at level three. I think GNP call with 'STLOCSEG*F ' will try to get first child under the current parent i.e. parent at level 2.
That is my understanding and I tried to make it by the description you have given.

I am new to IMS please correct if I am wrong.

Regards,
~Abhi

I'm guessing you've worked around this by now...

I think that the F command code will back up to the parent of the segment, not the "parent" that you established with the call to the root. Those are two different things.

Establishing parentage is more often concerned with keeping track of where you are in a list of twin segments. In your example, the place of interest would be the ITEM segments.

The good news is that using a GU to back up to the root again will almost certainly NOT require additional I/O. The database record is still in memory, and IMS will just use the buffer.

Hello Ed -

I am still confused and haven't really worked this out. I know, that the F Command Code is used to back up in the database. I do not understand, how the Parentage is lost.

Background
1. GU Call to Establish Parentage at [001 INDUS CHEMICALS] - Vendor

2. GNP Calls with unqualified SSA at STLOCSEG - Stock Segment Level 3, until Status-code='GE'


Database Position
At this point, 3 GNP Calls were executed successfully, the 4th GNP Call sets STATUS-CODE='GE'. The below picture shows, what I feel is the established parentage, and my position in the Database. Correct me, if I am wrong.


My Question
What according to you should be the result of a GNP CALL, Unqualified SSA at Level 3, STLOCSEG, with the Command Code F?

The GNP shouldnt alter parentage unless you have a *P ....but you have taken a GE
KFB area will show what IMS was able to do .
Why not just qualify the root in the SSA then you know exactly what will happen

Hello -
Thank you everybody. It took me a couple of months, and several e-mails to understand that Parentage, is not the same as Parent.

As the F command code is for Level 3, the CALL will look at its PARENT at the LEVEL 2. It will then retrieve the First LEVEL 3 CHILD segment sub-ordinate to the current LEVEL 2 PARENT(Again, current is not the same as parentage).

PARENTAGE is still set at the ROOT Segment, and will not move to another ROOT, unless I issue another GN or GU CALL.

Thank you very much.