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DDI 4 RDF page with links to GitHub and other outputs (upper right box on page) RDFS/OWL Team
DDI- field level documentation http://www.ddialliance.org/Specification/DDI-Codebook/2.5/XMLSchema/field_level_documentation.html
DDI-L field level documentation https://www.ddialliance.org/Specification/DDI-Lifecycle/3.2/XMLSchema/FieldLevelDocumentation/
DDI-4 development site (the model) https://lion.ddialliance.org