function returning multiple values

[D063520]

Hello,

I hope this is the right place (if not, I'm happy to be redirected to the right one ; ) ). I want to implement a function like:

https://rdf4j.org/javadoc/3.1.0/org/eclipse/rdf4j/spin/function/spif/Split.html

Spin is deprectated and I think my problem is more general: "how to I implement a function that returns multiple values" like the Split function. In the documentation:

https://rdf4j.org/documentation/tutorials/custom-sparql-functions/

this is not really described. I thought I should implement a TupleFunction instead of a Function and put the name in META-INF/services/org.eclipse.rdf4j.query.algebra.evaluation.function.TupleFunction. But the function is not seen. Not sure if this should work or maybe only work in combination with spin which is deprecated.

Any idea?

Merci!

D063520

[Jeen Broekstra]

This should work, except there is one extra bit needed, which is that you need to configure your backend SAIL to use a ExtendedEvaluationStrategy instead of the default evaluation strategy. For example, if you're using a MemoryStore, you can do something like this:

MemoryStoreConfig storeConfig = new MemoryStoreConfig();

storeConfig.setEvaluationStrategyFactoryClassName(ExtendedEvaluationStrategyFactory.class.getName());

RepositoryImplConfig repConfig = new SailRepositoryConfig(storeConfig);

SailRepositoryFactory factory = new SailRepositoryFactory();

Repository rep = factory.getRepository(repConfig);

This is a hassle, admittedly, and we're looking into simplifying it (see https://github.com/eclipse/rdf4j/issues/635).

As an aside, despite SPIN being deprecated, one of the things we do want to preserve is its set of custom (tuple) functions, because they can be useful even outside of a SPIN context. If you're interested in helping out, we welcome contributors!

Cheers,

Jeen