Since our inception in 1995, the DDI Alliance has developed work products to meet the evolving needs of our user communities and changes in technology. Our stable work products include:
DDI-Codebook (DDI 2) – an XML structure for describing codebooks (or data dictionaries), for a single study.
DDI-Lifecycle (DDI 3) – an XML structure that expands on the coverage of a single study along the data lifecycle and can describe several waves of data collection, and even ad hoc collections of datasets grouped for the purposes of comparison.
The Alliance continues to support, develop, and encourage the adoption of these specifications.
At the same time, the Alliance is continuing development to meet new user and technology needs, especially to address limitations of the standard. Our newest development is what we are calling DDI 4 and will be very different from earlier DDI work products because it will be based on an information model of the metadata content. This information model will be available for implementation in standard RDF vocabularies and standard XML structures, which will be equivalent. This form of model-based standard is a best practice in the world of standardization, and several other standards in other domains have been using this approach for many years. Developing DDI 4 is a way of protecting the standard against technological change, and a way of guaranteeing alignment across different technology implementations. 
Work on DDI 4 has been underway for several years and we are planning to release a prototype of the specification in mid-2018. This preliminary version is not intended for production but will provide an opportunity to test and provide feedback on how the DDI 4 model describes and documents some basic research material, such as a dataset, an instrument, and a codebook. A specific list of possible use cases will be made available to review and apply once the prototype is released.
The Alliance will provide additional information about the prototype release in the coming months. In the meantime, feel free to contact firstname.lastname@example.org with questions.
DDI Alliance Executive Board
Steve McEachern, Australia Data Archive (Chair)
William Block, Cornell Institute for Social and Economic Research (Vice Chair)
Catherine Fitch, Minnesota Population Center
Dana Müller, Research Data Centre of the Federal Employment Agency, Institute for Employment Research
Barry Rader, University of Wisconsin-Madison
Joachim Wackerow, GESIS - Leibniz Institute for the Social Sciences
Margaret Levenstein, Inter-university Consortium for Political and Social Research (ICPSR)
Jared Lyle, ICPSR and DDI Alliance Director (ex officio)