For the MODS schema there were several originally
locally-defined elements that people wanted to reference in other schemas. We
easily globalized those in MODS, and I don't see any reason not to do so for
For example, changing:
is a transparent change (it doesn't affect any
instances). It doesn't help schema readability, and so I wouldn't suggest doing this for all local elements, only
those specifically requested.
For MODS we've been making changes like these for
minor version changes. I would suggest for PREMIS version
1.1 globalizing any such elements specifically requested, such as
eventType, and after 1.1 is frozen, if someone requests globalization of an
element, put it in the queue for the next revision, and if it is an urgent
request, define a new minor revision.
----- Original Message -----
Sent: Friday, September 16, 2005 7:45
Subject: [PIG] Schema style (or, Extent and
> Hi all
> Here's a slightly more meaty style issue for
> I would like to extend the PREMIS schema in
at least one simple way: I
> want to restrict the content for
event.eventType to a handful of locally
> meaningful values. Ideally that
would also involve further refining the
> element into something like
eventSuperType and eventSubType, which suits
> my needs, though it
needn't trouble the global PREMIS schema.
> I'd like to be able
to define these (and other) extensions as local
> refinements of
PREMIS.xsd. I'd therefore expect to be able to create a
> local schema
that simply includes/imports all the definitions of
> PREMIS.xsd, and
then specifies a few redefinitions.
> XML Schema offers a way to
do this with <xs:redefine>. However, as far
> as I can see,
<xs:redefine> only works for type definitions, not element
definitions. Since all the PREMIS schema documents use a "Russian doll"
style, defining each element locally, rather than defining global types
separately and referencing them, it doesn't look like I'm going to be
able to do this.
> Is this something that might be remedied
soonish? If not, has anyone any
> ideas on how else I might achieve my
aims, without having to manage a
> complete local rewrite of PREMIS.xsd -
or convert to Relax NG!?
> PS. FYI, Ch
13 of Eric van der Vlist's XML Schema book (O'Reilly) has a
description of schema style alternatives, and their consequences
> \ Richard M
> / Digital Archives Specialist
> \ University of London
> / Tel: +44 (0) 20 7692 1350
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