Mainframe - IMS DC support

Introduction

The IMS/DC (Data Communications) system provides users with online "real time" access to information in IMS databases. MPP transaction programs are NOT submitted with OS JCL. The online IMS Control Region automatically schedules the MPP program necessary to process a transaction. This page summarizes how the Mainframe Analyzer handles IMS/DC.

Prototype link between GSAM DBD and JCL dataset

Inside a PSB file, the PCB connects to the database:

         PCB TYPE=GSAM,DBDNAME=GSAM01,PROCOPT=A,PCBNAME=GSAPCB
                                                                                 
*-------------- PSBGEN ----------------------------------------------*  
         PSBGEN LANG=COBOL,PSBNAME=COBIMSB1                              
         PRINT NOGEN      

Then we have the definition of the DBD IMS file:

         DBD   NAME=GSAM01,ACCESS=(GSAM,BSAM),                       X
               VERSION='09/22/0812.01'
DSG1     DATASET DD1=GSAM01,                                         X
               DD2=GSAM01,RECFM=FB
         DBDGEN
         FINISH

This IMS file calls the dataset of the JCL file, that calls the PSB file. The logic dataset name is set as GSAM01 and this is found when creating the JCL dataset:

//COBOLB1  EXEC PGM=DFSRRC00,PARM='DLI,COBIMSB1,COBIMSB1'
//STEPLIB  DD DSN=SYSCAST.IMS.SDFSRESL,DISP=SHR
//*                                      * IMS DBD AND PSB LIBS
//IMS      DD DSN=APPCAST.IMS.PSBLIB,DISP=SHR
//         DD DSN=APPCAST.IMS.DBDLIB,DISP=SHR
//*                                      * IMS STATISTICS
//DFSSTAT  DD  SYSOUT=P
//*                                      * IMS SYSTEM LOG
//IEFRDER  DD  DUMMY
//GSAM01   DD  DSN=MYTELCO.IMSGSAM.DATA,DISP=OLD

The Mainframe Analyzer will handle this scenario by linking the IMS file to the JCL dataset via a prototype link:

IMS Transaction Manager file

The Mainframe Analyzer will analyze the IMS Transaction file (*.tra) to resolve two macros:

• APPLCTN macro

• TRANSACT macro

Call link between Cobol Program and IMS Transaction

Code example:

APPLCTN PSB=IMMMBHI,PGMTYPE=TP,SCHDTYP=PARALLEL 06036000
TRANSACT CODE=IMMMBHI,MSGTYPE=(MULTSEG,RESPONSE,65), *06037000
PARLIM=0,SEGNO=400, *06038000
MODE=SNGL,PROCLIM=(03,01) 06039000

In this example, when the TRANSACT macro is created as code, the Mainframe Analyzer will create an IMS transaction object with the code name, then link it to the Cobol program named as PSB = XXX inside the APPLCTN macro.

IMS Transaction Flow

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The input data from the terminal is read by the data communication modules. After editing by MFS, if appropriate, and verifying that the user is allowed to execute this transaction, this input data is put in the IMS message queue. The messages in the queue are sequenced by destination, which could be either transaction code (TRAN) or logical terminal (LTERM). 

• I/O PCB - in a CICS-DBCTL environment, an input/output PCB (I/O PCB) is needed to issue DBCTL service requests. Unlike other types of PCB, it is not defined with PSB generation. If the application program is using an I/O PCB, this has to be indicated in the PSB scheduling request, as explained in Format of a PSB.
• Alternate TP PCB(s) - an alternate TP PCB defines a logical terminal and can be used instead of the I/O PCB when it is necessary to direct a response to a terminal. Alternate TP PCBs appear in PSBs used in a CICS-DBCTL environment, but are used only in an IMS/VS DC or IMS™ TM environment. CICS applications using DBCTL cannot successfully issue requests that specify an alternate TP PCB, an MSDB PCB, or a GSAM PCB, but PSBs that contain this kind of PCB can be scheduled successfully in a CICS-DBCTL environment. Alternate PCBs are included in the PCB address list returned to a call level application program. The existence of alternate PCBs in the PSB can affect the PCB number used in the PCB keyword in an EXEC DLI application program, depending on whether you are using CICS online, batch programs, or BMPs

Example

From a Cobol file, the Alternal-PCB contains the destination code (IMS Trans code or LTERM code). Example ALT-PCB:

       01  GNSALTIO-PCB.
           02  GNSALTIO-DESTCODE       PIC  X(008) VALUE 'ICLRSELT'.
           02  GNSALTIO-IMS-RESERVED   PIC  X(002).
           02  GNSALTIO-STATUS-CODE    PIC  X(002).
           02  GNSALTIO-CURRENT-DATE   PIC S9(007)  COMP-3.
           02  GNSALTIO-CURRENT-TIME   PIC S9(007)  COMP-3.
           02  GNSALTIO-MSG-SEQ-NUMBER PIC S9(008)  COMP.
           02  GNSALTIO-MOD-NAME       PIC  X(008).
           02  GNSALTIO-USER-ID        PIC  X(008).

Only the CHNG DLI Call could change the value of destination code. The ISRT DLI Call will send the message to LTERM or IMS Transaction:

Click to enlarge