Using Text Units to Customize BDT Transaction Processing

For each parameter specified on a transaction, BDT builds a control block called a text unit. These text units describe the processing to be done for the transaction as a whole or the processing to be done specifically for the TO or the FROM data set.

BDT puts the text units in the master job definition (MJD) for the transaction. Exit routine BDTUX08 can be used to define user transaction parameters that can be used to create text units. Before a transaction is placed on the BDT work queue, exit routine BDTUX19 can be used to add text units to the MJD. BDTUX19 can also be used to inspect and modify text units already in the MJD.

BDT processes two kinds of text units:

Dynamic allocation text units
These text units are created from parameters specified either in the TO section or the FROM section of a transaction. (For a description of the sections of a BDT transaction, refer to z/OS BDT File-to-File Transaction Guide.) For example, dynamic allocation text units are created for the VOLUME and the DSORG transaction parameters. Dynamic allocation text units are always considered to be nongeneric: that is, each pertains either to the TO data set or to the FROM data set, not to the transaction as a whole. Dynamic allocation text units are defined by MVS allocation services. BDT passes them to allocation services via SVC 99 to allocate the source and the destination data sets. Refer to z/OS MVS Programming: Authorized Assembler Services Guidefor information about dynamic allocation text units in MVS.
BDT text units
These text units are created from parameters specified in the job definition, the TO, or the FROM section of a transaction. A BDT text unit can describe either processing for the whole transaction (a generic text unit) or processing specifically related to the TO or the FROM data set (a nongeneric text unit). For example, generic BDT text units are created for the JOBNAME and MSGCLASS transaction parameters. Nongeneric BDT text units are created for the LOCATION and BDTENQ transaction parameters. BDT text units are not passed to SVC 99 to allocate a data set. They are used by BDT in its processing of the transaction.

Each text unit created for a transaction is identified by a key. Macro IEFZB4D2 maps the key values for dynamic allocation text units. Macro BDTDMJD maps the key values for BDT text units. User exit routines that have access to the MJD can use the BDTXTUAM macro to retrieve a particular text unit by specifying its key. Refer to BDTXTUAM for a description of how to use the BDTXTUAM macro.

You can create your own transaction parameters and associated text units that specify processing unique to your installation. This can be done by using the BDTDKYWD macro in BDTUX08, the language processor keyword extension table. This table extends BDT’s keyword table that defines valid transaction parameters and the text unit table that describes the corresponding text unit for each keyword. Note that BDTUX08 does not contain executable code; its purpose is to add entries to the keyword and text unit tables. Refer to the description of BDTUX08 in BDTUX08—User-Defined File-to-File Transaction Keywords and the description of the BDTDKYWD macro in BDTDKYWD.

You can also add text units to the MJD during transaction processing with BDTUX19, the transaction modification exit routine. BDTUX19 receives control from the language processor after it has processed all available transaction parameters. (Note that BDTUX19 will receive control twice: once in the user’s address space (or in BDT’s address space for some transactions entered at MCS consoles), and again in BDT’s address space after the language processor has processed the parameters specified in the GMJD library.) In BDTUX19 you may process the text units created in BDTUX08 for your installation-unique parameters. You may also inspect, modify, or add any other text units. See the description of BDTUX19 in BDTUX19—File-to-File Transaction Modification for a discussion of the functions this exit routine may perform.

After BDTUX19 is invoked in the BDT address space to make any final changes to a transaction, the transaction is written to the BDT work queue. Subsequent user exit routines may retrieve text units via BDTXTUAM and inspect them, but they may not change existing text units or add new ones.