I've no idea what ribbons are, but I suspect the URIs that you are referring to are namespace declarations. They are URIs rather than URLs - names rather than addresses - nothing more than unique identifiers for an XML vocabulary. XML parsers aren't going to go chasing around the internet to dereference them.
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference