RDF Equivalence Group

An Implementation Languages Workshop was held in Paris in December of 2022. One of the recommendations that came out of that meeting was to create an RDF “union” model that shows equivalent RDF classes across the various RDF representations of DDI products, including SDTL, XKOS, the next DDI Lifecycle version, and the upcoming DDI CDI. 

Equivalent classes help to express the same concept using different terms or combinations of properties within the DDI products. This makes the combined usage of the ontologies more semantically clear and allows for more intuitive querying and reasoning. Equivalent classes can facilitate alignment efforts by identifying semantically equivalent concepts in the different DDI product ontologies.

Current Work Plan:

  • Create and maintain an owl ontology with common class mappings

  • Show a proof of concept for sparql query expansion, querying across mapped products

  • Investigate expanding the scope to equivalent properties if the equivalent classes show usefulness

  • Explore mapping common DDI classes to other non-DDI ontologies such as schema.org


  • Dan Smith - Colectica (initial chair)

  • Flavio Rizzolo - Statistics Canada

  • Christophe Dzikowski - INSEE

  • Wendy Thomas

  • Arofan Gregory

  • MiYoung Choi

2024-2026 Tasks:

A Github repository will be created in the DDI Alliance organization to hold the work outputs and to perform issue tracking.
Set up a workgroup page on the DDI Jira
Send an announcement email to the DDI list serves asking for additional participants with an interest in the RDF vocabularies.
An initial kickoff meeting will be held with participants who expressed interest once the CDI, DDI Lifecycle 4, and SDTL 2 rdf vocabularies are available.
Develop a process to receive candidate equivalences
Develop an approval process to ratify and publish candidate equivalences.
Set up Continuous Integration for processing the SSSOM tsv files
Generation of OWL reified axioms
Generation of documentation for the upcoming https://docs.ddialliance.org site.