Public Review: Structured Data Transformation Language (SDTL)

The DDI Alliance is pleased to announce the Public Review of Structured Data Transformation Language (SDTL), a new product in the DDI suite of products that provides a key component of an automated metadata production process.
SDTL is an independent intermediate language for representing data transformation commands.  Statistical analysis packages (e.g., SPSS, Stata, SAS, and R) provide similar functionality, but each one has its own language and syntax.  SDTL consists of JSON schemas for common operations, such as RECODE, MERGE FILES, and VARIABLE LABELS.  SDTL provides machine-actionable descriptions of variable-level data transformation histories derived from any data transformation language.  Provenance metadata represented in SDTL can be added to documentation in Data Documentation Initiative (DDI) and other metadata standards.

SDTL greatly enhances the value of DDI; currently, DDI metadata is almost always created by data repositories but not by data producers.  Even when data are born digital, data producers discard provenance information that could be transported into DDI, because they perform data management and variable transformations in statistical packages that offer minimal metadata capabilities.  SDTL and the tools created by the C2Metadata Project are designed to create a metadata life cycle that parallels the research data life cycle. The same scripts that are used to transform and manage variables and data files can be used to update metadata files.  As a result, data producers can create more accurate and complete DDI metadata with less time and effort for them and for data repositories.

Links to the specification and instructions for comment are found at  We are eager to obtain feedback from a broad community on this specification. The comment period is open until August 31, 2020, and we hope to hear from you. Comments are requested on the content and scope of the:

  • SDTL Command Language
  • Function Library
  • Pseudo-Code Library
  • Documentation