Why ACB is required for online region.

abdulrafi · Posted: Thu Dec 03, 2009 10:00 am

As I knew there are 3 types of control blocks DBD,PSB,ACB.

DBD(Data Base Descriptor or Decription) specifies Physical
structure of an IMS database.
PSB ( Program Specification Block) Specifies Logical
Structure of an IMS database.
ACB The combination of DBD and PSB is nothng but ACB
(Application Control Block).

Can anybody please let me know why Online region alone requires an ACB and why not for a batch application (DL/I)?.

Also usually for batch aplication we specify the PSB we use near DFSCRC00 but for Online as it is combined in ACB could you please help me to identify where the library would be defined for online application.???????

PeterHolland · Posted: Thu Dec 03, 2009 10:29 am

ACB can have 2 types :

1. Dynamic: Which is used for IMS DB programs as the ACB
constructs at run time by giving respective DBDGEN and
PSBGEN.
2. Static : Which is used for IMS DC programs as the ACB
need to be created before executing the IMS DC program.

abdulrafi · Posted: Thu Dec 03, 2009 12:00 pm

Hi,

Thanks for your reply.

Suppose if I don't use ACB for IMSDC and if I use only DBDGEN, PSBGEN will my IMSDC application work fine?.

Also like batch we give the library in the jcl, for IMSDC if ACB is necessary, whether it would be given in the format library internally?.
If not could you please how and where it will be defined?

Thanks

PeterHolland · Posted: Thu Dec 03, 2009 12:45 pm

ACB is a consolidation of PSB and DBD information.

• For online programs
ACBs must be prebuilt using the ACBGEN utility i.e., ACBGEN must
be run which will merge DBD and PSB and generate ACB.

• For batch programs
ACBs can be generated either at execution time
(dynamically using IMS.DBDLIB and IMS.PSBLIB as input (PARM=DL/I))
or ahead of time (prebuilt ACB from IMS.ACBLIB can be used (PARM=DBB)).

ACB's are part of IMSDC (you cant run IMSDC without an ACBLIB).