Application data structure terminology

Application data structure

The application data structure is the copybook generated during assembly of a BMS map. It has the mnemonic ADS, and it can be created in short form or long form. You will sometimes see the long form referred to as ADSL.

The short form of the ADS has fields that are not fullword aligned, whereas the long form of the ADS has all its fields fullword aligned.

The short form of the ADS is generated by default by map assembly. In order to obtain the long form of the ADS, you must assemble your BMS maps with the following parameters specified in the DFHMSD macro:

MSETNAM   DFHMSD

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DSECT=ADSL,        *
LANG=C,            *

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If you examine the DSECT that is produced on map assembly, you will see that all of the fields are fullword aligned. Be aware that this significantly increases the size of the application data structure and any message which includes it.

This option is only available for programs written in the C-language. However, It is possible to create COBOL data structures from such a DSECT by manually creating them. The redbook CICS Transaction Server for OS/390 Version 1 Release 3: Web Support and 3270 Bridge gives examples of this.

Application data structure descriptor

The application data structure descriptor is an architected structure that allows an application to interpret the application data structure in a vector without having access to the copybook generated during map assembly.

There are two forms of the application data structure descriptor:

• The application data structure descriptor in short form contains fields that are not fullword aligned. It has the mnemonic ADSD.
• The application data structure descriptor in long form contains fields that are all fullword aligned. It has the mnemonic ADSDL.

ADSL - an ambiguous mnemonic

The mnemonic ADSL is ambiguous, and is sometimes used to refer to the application data structure in long form, and sometimes the application data structure descriptor in long form. The correct mnemonic for the application data structure descriptor, long form, is ADSDL. However, if you look at the eye-catcher in the ADSDL you will see that it is ADSL, which leads to the ambiguity. The correct use of ADSL is to describe the application data structure, not its descriptor, in long form.