Over the past several years a number of methods have been developed to describe data. The debugger created XML mapping files. SDO created a metadata file. Business events and Operational Decision Management created the TPF Data Model. None of these descriptions were standard however and as such only worked with a particular area on z/TPF. Data Format Description Language (DFDL) provides a standardized way of describing data. This description can be supported not only on z/TPF but other platforms, which means the same DFDL files can be used across platforms when describing the same data. Furthermore, z/TPF enhancements going forward can now use a common data description instead of reinventing something specific for a particular area. As such, business events has already been updated to support DFDL.
DFDL is based on XML Schema 1.0. DFDL annotations and attributes are added to an XML schema to create a better understanding of binary data. The DFDL information allows for descriptions of things like variable size fields, variable size arrays, and conditional structures and fields. Because it is based on XML schema, data described by DFDL can easily be transformed into a document such as XML or JSON. Alternatively, the DFDL APIs could also be used to access the data directly with a document perspective without having had to transform the information to a document.
To help you start creating DFDL schemas for your data, the ZUDFM DESCRIPTOR command can be used to create an initial DFDL schema file for z/TPFDF. These schema files should be further enhanced however to better describe the data (such as changing assembler dsect names to XML tag names or providing discriminators for multiple ORGs). After creating DFDL schema files to represent data, they can be loaded to /sys/tpf_pbfiles/tpf-fdes on a z/TPF system to make the information useable by the DFDL APIs.