Docbook 5 and olink

Hello,

I'm working with oXygen and DocBook version 5.0 with XInclude.

I'm trying to make links from a document to another file. I've tried with 
olink, but really don't understand what I should have in my olinkdb.xml file.

I don't either find a relax NG schema that I could apply to it.

Are there somewhere a documentation with some examples I could look at?

Thanks,
Ph. Faehndrich