Description of SDTL

There are currently three parts of SDTL:

1. SDTL has been developed as a set of JSON schemas, which describe data transformation commands and the expressions within commands, like variable names. SDTL JSON can be rendered in other formats, like XML and OWL RDF. SDTL documentation and downloads are available on Gitlab.

2. Function Library:  Each statistical package has hundreds of functions for common mathematical, statistical, and text operations, such as LOG, SINE, AVERAGE, and LENGTH.  The Function Library is a crosswalk between a standard SDTL representation of each function and the implementations of that function in various statistical languages. The Function Library minimizes program code for SDTL applications, because all functions can be handled in the same way, and additions to the Function Library do not require changes to program code.

3. Pseudocode Library:  The Pseudocode Library provides human readable translations of SDTL commands.  Like the Function Library, it is external to the SDTL JSON schemas, so it minimizes program code and can easily be updated. 

The C^​2​Metadata Project has developed software applications based on SDTL:

1. Parsers for SPSS, Stata, SAS, R, and Python translate command scripts in these languages into SDTL

2. Updaters for DDI and Ecological Markup Language (EML) incorporate SDTL into existing metadata files

3. A Pseudocode Generator translates SDTL commands into human-readable text

4. A Codebook Formatter reads SDTL-enhanced DDI Codebook XML, and creates an interactive HTML codebook that displays variable-level provenance metadata with hyperlinks to antecedent versions of variables.

These applications are prototypes to demonstrate the potential of SDTL, which will be available as open source code.  We expect software developers to incorporate these functions into future products.

Please note that SDTL is currently limited to describing data transformations.  A similar approach to statistical analysis is possible, but beyond the scope of our current project.