Unload an IMS Database

You must unload the IMS database into a sequential file as follows:

The file must contain variable-length records
Each record must contain one segment
Each record must contain the record length, segment name, and segment data in fixed positions

We recommend that you use one of the following methods to unload the database:

Standard IBM unload utility for IMS/ESA

The standard IBM unload utility creates a sequential file with a variable-length record for each segment. In each record, the segment name begins in position 7 and the segment data begins in position 36. In this case, you must use either VRECGEN or Mainframe Access to download the file in order to preserve record length data.

Enterprise Developer IMSDBUV utility

The IMSDBUV utility enables you to unload an IMS database into a segment layout that provides for simpler loading of the migrated database. The physical characteristics of the file and data are stored in header and trailer records in the file. This includes items such as the placement of the segment name, segment data, and compression options.

The IMSDBUV utility is provided as a COBOL program file, IMSDBUV.CBL, and JCL, IMSDBUV.JCL. Both files are located in your $COBDIR/demo/Mainframe/IMS/Classic/Examples directory by default.

Note: We also supply the IMSDBUC.CBL compressed program in the same directory.

The IMSDBUV program executes as a BMP or stand-alone DLI program using an application PSB. The IMSDBUV JCL contains sample JCL for running this program. It retrieves segments from a database. For each segment, it creates a variable-length record containing record length, segment name, and segment data.

We provide several options when using the IMSDBUV utility. For example, you can optionally:

Use the IMSDBUC.CBL compression program in conjunction with IMSDBUV.CBL
Add information such as the compression routine used
Decompress input and compress output files on a PC platform via the provided CBLDCIMS routine
Write a program to perform different segment encoding on a PC platform, enabled using the COMPRESS directive

Complete instructions for using the IMSDBUV utility are contained in the IMSDBUV.CBL file. The basic process is as follows:

Transfer the IMSDBUV.CBL, IMSDBUV.JCL, and optionally the IMSDBUC.CBL files to your mainframe.
Compile IMSDBUV.CBL on your mainframe.
Edit the IMSDBUV.JCL, replacing the embedded question marks (?) with your system information.
Run the compiled code via IMSDBUV.JCL.

When you use IMSDBUV, you can download the generated file using any download utility, such as FTP, to perform a binary download.

Third-party unload utility

You can use a third-party unload utility provided it generates an output file that meets the migration requirements. In this case, you must use either VRECGEN or Mainframe Access to download the file in order to preserve record length data.