Metadata question

Hello All,

As a long time accessibility specialist who's been involved in W3C work for
more than 15 years, I am now getting involved with accessibility in ePub
(thanks to a new contradict), and while accessibility principles are
old-hat to me, some of the peculiarities of epub packaging are still kind
of new to me.

While I hope to get more involved overall with epub+accessibility, at this
time I wonder if I may pose a question to the assembled experts on this
list? Specifically:

Currently epubcheck is telling me that there is an error with some of the
metadata in a specific opf file, but epubcheck doesn't tell me with enough
detail what the actual error is, only where to find it (sigh). This is the
problematic error message and metadata:

"Error while parsing file: Property "identifier-type" must refine an
"identifier" or "source" property"

*<dc:subject xmlns:html="http://www.w3.org/1999/xhtml
<http://www.w3.org/1999/xhtml>" id="subject01">Marketing</dc:subject>*
*<meta xmlns:html="http://www.w3.org/1999/xhtml
<http://www.w3.org/1999/xhtml>" refines="#subject01"
property="identifier-type" scheme="onix:codelist26">10</meta>*


My *assumption* at this time is that the issue here is that this code is
attempting to refine the dc:subject with an onix 'term', but... (?)

Questions:

   - Can Dublin Core and Onix metadata live together in harmony in the opf
   file?
   - Am I correct in my assumption that the actual error is the
   "cross-linking" of the two schemes?
      - ...and would the remediation path be to remove the
      refines="#subject01" entry from the second declaration?
   - Or am I completely missing the boat and looking in the wrong place? Is
   this correct in principle, but incorrect in implementation?

Any light anyone can shed on this would be appreciated - references would
be an absolute bonus - but today I'd be happy to just understand what to do
to fix this.

Thanks in advance!

JF
-- 
*John Foliot* | Senior Industry Specialist, Digital Accessibility

"I made this so long because I did not have time to make it shorter." -
Pascal "links go places, buttons do things"