Use Case Accelerators > Mainframe Data Offload

Mainframe Data Offload

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One of the challenges of offloading mainframe data to an open system is determining how to interpret the data. A COBOL copybook typically provides the record structure of a mainframe dataset, but interpreting the contents of a COBOL copybook, with various binary formats and REDEFINES clauses, is itself a challenge that few open source mechanisms can handle.

DMExpress easily connects to the mainframe, pulls the data, and both interprets and transforms it, all set up through a convenient graphical interface. It eliminates the file transfer and coding complexities of other tools such as JRecord.


Mainframe data sets generally contain numeric data stored in various binary formats, including packed decimals, zoned decimals, native binaries, and others, represented as COMP types in COBOL copybooks. Typically, these copybooks also contain a number of REDEFINES clauses, each of which imposes its own interpretation on the same set of bytes.

For example, if two REDEFINES are applied to an 8-byte text field [PIC X(8)], those 8 bytes can be interpreted in three different ways, such as a transaction date that can be used for US date format, UK date format, or a summary date format.

Unfortunately, the logic for choosing the correct interpretation during record processing is embedded in the COBOL program on the mainframe, not in the copybook. This means the interpreting system must provide a way to handle this ambiguity when migrating mainframe datasets to open systems.

Here we compare the benefits of using DMExpress to process mainframe files over using a tool such as JRecord.

Additional Information

For an example of using DMExpress to process mainframe datasets, see DMX-h Use Case Accelerator: Extract Mainframe Files with REDEFINES To HDFS.

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