Hi Egon, please see my answers inline. On Tue, Jun 11, 2024 at 4:39 PM Egon Willighagen <[email protected]> wrote:
> > Hi, thank you for the update. > > The email writes that "Queries that need federation will need to be > rewritten. You can ask for help to rewrite queries". > > Do you have guidelines on how to do this? It took quite some effort to > make some of the (I thought simple) queries work, but later improvements > showed more workable. How were they developed? How do people rewrite the > SPARQL queries when two or more query triples are distributed over the two > SPARQL endpoint, and particularly when they depend on each other? > > We wrote some general documentation at https://www.wikidata.org/wiki/Wikidata:SPARQL_query_service/WDQS_graph_split/Federation_Limits including some explanation of how federation works underhood, the limitations and some common mistakes I have made when rewriting queries. https://www.wikidata.org/wiki/Wikidata:SPARQL_query_service/WDQS_graph_split/Federated_Queries_Examples is more concrete and have a dozen real world queries that we rewrote and some documentation on the process we went through when rewritting, it includes two scholia queries. A common pattern I often found to be useful is the use of UNION and properly identifying the triples selecting the publications. Hope it helps, David
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