IMS DB - DL/I Functions

DL/I function is the first parameter that is used in a DL/I call. This function tells which operation is going to be performed on the IMS database by the IMS DL/I call. The syntax of DL/I function is as follows −

01 DLI-FUNCTIONS.
   05 DLI-GU        PIC X(4)    VALUE  GU   .
   05 DLI-GHU       PIC X(4)    VALUE  GHU  .
   05 DLI-GN        PIC X(4)    VALUE  GN   .
   05 DLI-GHN       PIC X(4)    VALUE  GHN  .
   05 DLI-GNP       PIC X(4)    VALUE  GNP  .
   05 DLI-GHNP      PIC X(4)    VALUE  GHNP .
   05 DLI-ISRT      PIC X(4)    VALUE  ISRT .
   05 DLI-DLET      PIC X(4)    VALUE  DLET .
   05 DLI-REPL      PIC X(4)    VALUE  REPL .
   05 DLI-CHKP      PIC X(4)    VALUE  CHKP .
   05 DLI-XRST      PIC X(4)    VALUE  XRST .
   05 DLI-PCB       PIC X(4)    VALUE  PCB  .

This syntax represents the following key points −

For this parameter, we can provide any four-character name as a storage field to store the function code.

DL/I function parameter is coded in the working storage section of the COBOL program.

For specifying the DL/I function, the programmer needs to code one of the 05 level data names such as DLI-GU in a DL/I call, since COBOL does not allow to code pterals on a CALL statement.

DL/I functions are spanided into three categories: Get, Update, and Other functions. Let us discuss each of them in detail.

Get Functions

Get functions are similar to the read operation supported by any programming language. Get function is used to fetch segments from an IMS DL/I database. The following Get functions are used in IMS DB −

Get Unique

Get Next

Get Next within Parent

Get Hold Unique

Get Hold Next

Get Hold Next within Parent

Let us consider the following IMS database structure to understand the DL/I function calls −

Get Unique

GU code is used for the Get Unique function. It works similar to the random read statement in COBOL. It is used to fetch a particular segment occurrence based on the field values. The field values can be provided using segment search arguments. The syntax of a GU call is as follows −

CALL  CBLTDLI  USING DLI-GU
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

If you execute the above call statement by providing appropriate values for all parameters in the COBOL program, you can retrieve the segment in the segment I/O area from the database. In the above example, if you provide the field values of Library, Magazines, and Health, then you get the desired occurrence of the Health segment.

Get Next

GN code is used for the Get Next function. It works similar to the read next statement in COBOL. It is used to fetch segment occurrences in a sequence. The predefined pattern for accessing data segment occurrences is down the hierarchy, then left to right. The syntax of a GN call is as follows −

CALL  CBLTDLI  USING DLI-GN
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

If you execute the above call statement by providing appropriate values for all parameters in the COBOL program, you can retrieve the segment occurrence in the segment I/O area from the database in a sequential order. In the above example, it starts with accessing the Library segment, then Books segment, and so on. We perform the GN call again and again, until we reach the segment occurrence we want.

Get Next within Parent

GNP code is used for Get Next within Parent. This function is used to retrieve segment occurrences in sequence subordinate to an estabpshed parent segment. The syntax of a GNP call is as follows −

CALL  CBLTDLI  USING DLI-GNP
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

Get Hold Unique

GHU code is used for Get Hold Unique. Hold function specifies that we are going to update the segment after retrieval. The Get Hold Unique function corresponds to the Get Unique call. Given below is the syntax of a GHU call −

CALL  CBLTDLI  USING DLI-GHU
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

Get Hold Next

GHN code is used for Get Hold Next. Hold function specifies that we are going to update the segment after retrieval. The Get Hold Next function corresponds to the Get Next call. Given below is the syntax of a GHN call −

CALL  CBLTDLI  USING DLI-GHN
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

Get Hold Next within Parent

GHNP code is used for Get Hold Next within Parent. Hold function specifies that we are going to update the segment after retrieval. The Get Hold Next within Parent function corresponds to the Get Next within Parent call. Given below is the syntax of a GHNP call −

CALL  CBLTDLI  USING DLI-GHNP
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

Update Functions

Update functions are similar to re-write or insert operations in any other programming language. Update functions are used to update segments in an IMS DL/I database. Before using the update function, there must be a successful call with Hold clause for the segment occurrence. The following Update functions are used in IMS DB −

Insert

Delete

Replace

Insert

ISRT code is used for the Insert function. The ISRT function is used to add a new segment to the database. It is used to change an existing database or load a new database. Given below is the syntax of an ISRT call −

CALL  CBLTDLI  USING DLI-ISRT
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

Delete

DLET code is used for the Delete function. It is used to remove a segment from an IMS DL/I database. Given below is the syntax of a DLET call −

CALL  CBLTDLI  USING DLI-DLET
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

Replace

REPL code is used for Get Hold Next within Parent. The Replace function is used to replace a segment in the IMS DL/I database. Given below is the syntax of an REPL call −

CALL  CBLTDLI  USING DLI-REPL
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

Other Functions

The following other functions are used in IMS DL/I calls −

Checkpoint

Restart

PCB

Checkpoint

CHKP code is used for the Checkpoint function. It is used in the recovery features of IMS. Given below is the syntax of a CHKP call −

CALL  CBLTDLI  USING DLI-CHKP
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

Restart

XRST code is used for the Restart function. It is used in the restart features of IMS. Given below is the syntax of an XRST call −

CALL  CBLTDLI  USING DLI-XRST
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

PCB

PCB function is used in CICS programs in the IMS DL/I database. Given below is the syntax of a PCB call −

CALL  CBLTDLI  USING DLI-PCB
                     PCB Mask
                     Segment I/O Area
                     [Segment Search Arguments]

You can find more details about these functions in the recovery chapter.