Observations on automated client-side query federation over Wikidata SPARQL endpoints

The recent Wikidata graph split divided a previously singular SPARQL endpoint into two distinct ones, breaking existing queries that depend on the combined data from these endpoints. To accommodate this graph split, instructions for manual source assignment have been provided. However, the proposed solution of manual source annotations within the queries themselves, through the use of SPARQL SERVICE clauses, not only imposes additional work on users of these endpoints, but also assumes prior knowledge of which data come from which endpoint, and how they should be combined. Potential future graph splits would result in this manual source assignment having to be done again. Within this work, we employ client-side query federation over the two Wikidata endpoints, using state-of-the-art source assignment approaches for query operations, to demonstrate the feasibility and challenges of automated federation as an alternative to manual source assignment. Through our experiments, we show how client-side federation can offer a viable alternative to manual source assignment for certain queries, where the amount of data to process remains within client-side resource limits, and provided no custom behaviour is attached to standard SPARQL operations. Future work will be needed to address the trade-offs between network request counts and client-side data processing, to be able to execute queries that access large amounts of data from multiple sources.

@inproceedings{hanski_wikidata_federation_2025,
  author = {Hanski, Jonni and Crum, Elias and Taelman, Ruben},
  title = {Observations on automated client-side query federation over Wikidata SPARQL endpoints},
  booktitle = {Proceedings of the Wikidata Workshop 2025 co-located with 24th International Semantic Web Conference (ISWC 2025)},
  year = {2025},
  month = nov,
  url = {https://www.rubensworks.net/raw/publications/2025/hanski_wikidata_federation_2025.pdf}
}