The Data Documentation Initiative (also known as DDI) is an international standard for describing surveys, questionnaires, statistical data files, and social sciences study-level information. This information is described as metadata by the standard.
Begun in 1995, the effort brings together data professionals from around the world to develop the standard. The DDI specification, most often expressed in XML, provides a format for content, exchange, and preservation of questionnaire and data file information. DDI supports the description, storage, and distribution of social science data, creating an international specification that is machine-actionable and web-friendly.
Version 2 (also called "Codebook") of the DDI standard has been implemented in the Dataverse data repository and the data archives of the Inter-university Consortium for Political and Social Research. The latest version 3.3 (also called "Lifecycle") of the DDI standard was released in 2020.