Converting Delta Formats

How to Convert Forward Delta Formats to Reverse Delta Formats
Conversion to reverse delta format should be planned carefully. The steps in conversion are summarized here, then described in detail in the following sections.
  1. Analyze existing types to determine which are likely to benefit from conversion.
  2. Resize and allocate new base libraries for these types.
  3. Resize the delta libraries.
  4. Evaluate and modify processors.
  5. Run a full unload for each environment.
  6. Adjust the definitions of these types to reflect the conversion. Make the necessary changes to the library names on the Type Definition panel.
  7. Reload by system to populate the new libraries.
  8. Run the Validate utility to confirm results.
Considerations When Converting Forward Delta Formats to Reverse Delta Formats
Consider the following when converting to reverse delta format to ensure your success:
  • Elements are stored in the new storage format after the first source UPDATE following the conversion.
  • Component lists are stored in the new storage format after the first GENERATE action is executed against the element following either a change in an input component or a source update.
  • The current delta format for an element appears on panel 1 of the Element Master display.
  • Source messages related to forward/reverse delta conversion are in SMGRnnnn format.
Analyzing Existing Types
Use reverse deltas for the types that:
  • Normally need a source output library but do not need to be backed out (
    does not backout/backin base/delta libraries).
  • Need to be kept in standard PDS format for utilities, such as Advantage
    File Master Plus
  • Are used exclusively on the workstation.
Types that can benefit from the reverse delta storage format include the following:
  • Copybooks
  • JCL
  • Source
Use forward deltas for types that:
  • Have no external access requirements.
  • Can benefit from being compressed.
  • Can benefit from being shared (encrypted).
Resizing and Allocating New Base Libraries
Since the element base is the current image in reverse delta format, separate base libraries are required for each type in a particular stage. When reallocating your base libraries, keep the following in mind:
  • Plan the library structure first. Keep a record of the plan for use when updating type definitions.
  • Confirm that LRECL, BLKSIZE, and RECFM parameters are appropriate to the type being converted (see the existing source output libraries).
  • Keep in mind non-compression when planning space requirements.
  • Plan for and allocate new base libraries for every type within a system. Confirm that the new libraries map properly to stage and type requirements.
  • When planning for workstation types, remember that most mainframe compilers require LRECL=80.
Resizing the Delta Libraries
Resize the delta libraries to account for movement of the base component list member to the delta library. The resizing requires space revisions to the file and the directory.
Evaluating and Modifying Processors
Evaluate your processors, keeping in mind the following:
  • The CONWRITE step can be eliminated when using reverse deltas.
  • The CONWRITE step, when used, needs to be modified to take account of revised Include libraries.
  • Processors can read the base library directly when reverse deltas are being used.
Running a Full Unload of Each Environment
To capture all elements, perform a full unload (BC1JUNLD) against each environment or, optionally, by system for large installations.
Adjusting Type Definitions
After unloading all affected elements, change the type definitions on the Type Definition panel for those types that you want to store in reverse delta format. Change the following:
  • FWD/REV DELTA field to 
  • SOURCE LENGTH, COMPARE FROM, and COMPARE TO fields to the desired values.
  • FWD/REV delta setting in the COMPONENT LIST OPTION field (optional).
  • Library definitions as necessary to reflect new base libraries and optional changes to include and source output libraries. Use the information recorded in Step 2.
Reloading Inventory by System
Execute the Reload utility (BC1JRELD) by system to populate the new libraries with your inventory.
Validating the Results
Execute the Validate utility (BC1JVALD) to confirm the results.
How to Convert a Forward/Reverse Delta to a Full-Image Delta
If you want to change the delta format of an existing type from forward/reverse to full image, and the type has elements associated with it, you must do the following:
  • Define a new type as full image delta format
  • Transfer the elements to the new type
If types are mapped with different delta formats, the WITH HISTORY option may or may not be an option. The following table shows when the WITH HISTORY option can be used for a MOVE or TRANSFER when types with different delta formats are mapped together:
Source Format
Target Format
MOVE with history
MOVE without history
TRANSFER with history
TRANSFER without history
Restore Action and Converting Delta Formats
The Restore statement restores an element from an archive data set back to
, copying the source as it was before the element was archived or transferred to the data set. Also, the Restore action can restore elements from an unload
You can use the Restore action to convert elements to different storage formats as follows:
  • Reverse delta elements to forward delta elements
  • Forward delta elements to reverse delta elements
  • Forward, reverse, or image delta elements to log delta elements
 For more information, see 
SCL Reference
How to Convert Elements to Log Delta Format
You can use the Restore action to convert forward, reverse, or image delta elements to log delta elements. Complete the following steps to convert to log delta format:
  1. Use the Transfer to Archive action with the Bypass Delete Processor option to archive the elements you want to change.
    This archives the element and component base and delta files in their current formats, deletes them from
    , but leaves the elements outputs.
  2. Change the Type definition to Log on the elements in their current location.
  3. Use the Restore action with the Bypass Generate Processor to restore the elements from the archive to the element's current location.
    The element delta type is changed to log format and the outputs are not changed.
     To retain the MCF generate information, also specify the Retain Generate History option. Without the Retain Generate History option, the Restore action reinitializes the generate MCF information and the prior information is lost.