Interesting dilemma. How are you expressing the rules for how the two
metadata "chunks" are to be recombined and used together? Does your
profile cover that? There's nothing that I know of in METS that would
say "Take the "creator" from dmdSec2 and "title" from dmdSec1" etc.
Imagining myself as someone who would receive your data (hypothetically)
I would probably prefer that a single logical set of metadata be
pre-combined in the record, each with its own namespace, rather than
have to combine them for, say, indexing or display. Without any special
knowledge of your profle, looking at a record I would assume that the
two metadata sets are each complete expressions of the description using
different rules. But without more particulars (i.e. how interdependent
are the data elements from the two "chunks") it's hard to know. Maybe
you could give us an example, even if it is a mocked-up one.


Robert Tansley wrote:

>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
>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

Karen Coyle / Digital Library Consultant
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