How to compare values, ignoring diacritics, with SPARQL

I've been trying (with no success so far) to filter values with a "broader equals" condition. That is, ignoring diacritics.

select * where {  
  ?s per:surname1 ?t.
  bind (fn:starts-with(str(?t),'Maria') as ?noAccent1) .
  bind (fn:translate(str(?t),"áéíóú","aeiou") as ?noAccent2) .
} limit 100

To this moment, I've tried with XPath functions fn:contains, fn:compare, fn:translate, fn:starts-with, but none of them seem to be working.

Is there any other way (other than chaining replaces) to add collation into these functions or achieve the same goal?

Solution

The XPath functions you mention are not part of the SPARQL standard really, so as you found out, you can't rely on them being supported out of the box (though some vendors may provide them as an add-on).

However, GraphDB (which is based on RDF4J) allows you to create your own custom functions in SPARQL. It is a matter of writing a Java class that implements the org.eclipse.rdf4j.query.algebra.evaluation.function.Function interface, and registering it in the RDF4J engine by packaging it as a Java Service Provider Interface (SPI) implementation.