Hello,
I also tried to use xml schemas for MusicXML or MEI in the past but could not understand a thing from the swi-prolog documentation.
In my case, I wanted to do automatic conversion of numbers from atom to prolog numbers when reading and writing xml, but I don’t think this is implemented at all.
Just for curiosity, could you tell us what kind of project are you using MusicXML and prolog for ?
In my case, I’m trying to write a pure bidirectional grammar of the common music notation.