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Hi all,

I have a question about the best way to embed some descriptive metadata in
METS.  It may be as much a plain XML question as a METS question.

First, some background:  I have a project in China that is connecting
DSpaces together (sharing/mirroring content and metadata) using METS (1.4)
over OAI-PMH, with content included via reference (i.e. a URL that the
DSpace doing the mirroring can retrieve).

The metadata requirements of the project aren't fulfilled by Dublin Core
alone.  Every item has a few core Dublin Core fields, and there are various
categories of object, each with some extended (non-DC) elements.

The question is, would it be useful to include the Dublin Core in its own
<dmdSec>, and have the extended metadata (with a separate XML schema) in a
separate <dmdSec>?  My initial suspicion was that having separate <dmdSec>s
would be useful because:

- Easier to do XML schema validation on each.  Is this true?  It's certainly
possible to 'mix' elements from different namespaces in a single <mdWrap>,
but I'm not sure of the implications for validation (which is pretty
important for this project I think.)

- Other systems that don't understand the extended metadata can at least use
the Dublin Core.  Though perhaps a separate dmdSec wouldn't make much
difference here, if the other system can pick out the understood elements
from the one <dmdSec>?  However I can see that a simple, general METS
profile might just be "METS with DC in a dmdSec", which means that our
project would conform to that (as well as our own more specific profile, of
course).

I'm also wondering whether the presence of two <dmdSec>s could confuse
people.  Both <dmdSec>s relate to the object as a whole, rather than an
individual file or group of files.  Also, they are complementary.  That is,
in order to get all the descriptive metadata about the object, you need the
contents of both; this is a different situation to where one dmdSec is a
crosswalk of the other (e.g. where one <dmdSec> has Dublin Core, and another
has "the same" metadata crosswalked into MODS).  Does the presence of two
<dmdSec>s imply or suggest anything?  Or is it purely up to the particular
profile/use of METS?

I guess I'm just wondering whether there is a best practice or any advantage
to one approach over the other.  Any comments welcome...

 Robert Tansley / Digital Media Systems Programme / HP Labs
  http://www.hpl.hp.com/personal/Robert_Tansley/