How to use CDBase URIs in Content MathML?

Dear all,

  I'm writing in response to an issue pointed out by Urs Holzer (Cc).  He said
that in http://www.w3.org/TR/MathML3/chapter4.html the csymbol/@cdbase
attribute is not documented.  Indeed, the only occurrence of the word "cdbase"
is in the definition of how URIs for OpenMath symbols are constructed.

But then, OTOH, the description in section 4.2.3.1 seems to suggest that
actually Content MathML does not have a direct counterpart to OpenMath's <OMS
cdbase="B" cd="C" name="N"/>.  We can only write <csymbol cd="C">N</csymbol>
and hope for one of the following:

* B is somehow set by the enclosing document
* there is a @cdgroup attribute on the <math> element that points to a "CD
  group file" – from OpenMath I know what such a file is, but in the relevant
  MathML spec section it is not really specified how that mechanism works.
  Section http://www.w3.org/TR/MathML3/chapter2.html#interf.toplevel.atts
  gives no reference to the specific section of the OpenMath spec, and Section
  4.2.3.1 does, though.
* B happens to be http://www.openmath.org/cd

OK, but I'm still confused:  How would I translate the following to Content
MathML?

<OMOBJ>
  <OMA>
    <OMS cdbase="http://example.org/cd" cd="foo" name="bar"/>
    <OMS cdbase="http://somewhere.com/cd" cd="foo" name="baz"/>
    <OMS cdbase="http://frobnitz.org/cd" cd="foo" name="fnord"/>
  </OMA>
</OMOBJ>

I.e. what do I do when one formula uses symbols from CDs that have the same
relative name but under different CDBase URIs?

And why is there no csymbol/@cdbase?

Cheers, and thanks,

Christoph

-- 
Christoph Lange, Jacobs Univ. Bremen, http://kwarc.info/clange, Skype duke4701