How to read a 'NULL' value from an IMS DB Segment

dmithunibm · New User Joined: 23 May 2007 Posts: 18 Location: Bangalore

Hello All,

Can anyone help me in the below issue.

'How to read a NULL value from an IMS Database segment through PLI programming.'

enrico-sorichetti · Posted: Tue Apr 22, 2008 2:24 pm

can You please elucubrate on the meaning of NULL

dmithunibm · New User Joined: 23 May 2007 Posts: 18 Location: Bangalore

We all know that in DB2 easily we can find out the columns with NULL.(.....WHERE COLNAME = 'NULL').

But what I wanted to know is whether there is a way of doing the same thing in IMS DB also.

enrico-sorichetti · Posted: Tue Apr 22, 2008 2:32 pm

You should remember that IMS/DB is not COLUMN/FIELD oriented,
it is SEGMENT/RECORD oriented

the only case were fields ( real or virtual ) are being define to IMS ( rough approach )
is when keys ( and similar ) are defined

dmithunibm · New User Joined: 23 May 2007 Posts: 18 Location: Bangalore

Hi Enrico,

I can understand.

But how to proceed in the case when there is a need to read an IMS Segment having a NULL value in one of it's fields.

Is it possible to have NULL value in any of the segment fields ?

Can you please explain me the same.

vasanthkumarhb · Posted: Tue Apr 22, 2008 2:42 pm

Hi,

there is no NULL concept in IMS data base

enrico-sorichetti · Posted: Tue Apr 22, 2008 2:45 pm

a NULL column is defined by conventions and additional info managed by the DB2 infrastructure

You must define Your own concept of NULL field for a record/segment oriented infrastructure
an approach would be for every nullable field to add into the segment/record a flag telling the fact,
but then You would have to add the logic for managing the null indicators

if Your application really need a NULLABLE entity I would meditate on using a segment on its own,
if the segment is not there then the entity is null, otherwise ....
To nullify such a field it would simply mean to delete the appriate segment

dmithunibm · New User Joined: 23 May 2007 Posts: 18 Location: Bangalore

Hi Enrico,Vasanth,

Thanks a lot for your valuable info :-)

Thanks & Regards,
Mithun.

Douglas Wilder · Posted: Tue Apr 22, 2008 8:48 pm

In some of our applications spaces in an otherwise numeric field is used to indicate "null" ie. sufficient data is not available to calculate the value for this field. This is different from the value being calculated as zero. In many ways I do not like this, but it fills the business need.

dick scherrer · Posted: Tue Apr 22, 2008 8:56 pm