On Wed, 19 Oct 2005, Brian Tingle wrote:
> On Wed, 2005-10-19 at 16:35, jeroen bekaert wrote:
> > Changing mandatory/optional occurence constraints based on METS related
> > issues is clearly an 'interoperability with other schemas' problem. Its
> > sole purpose is the trouble-free use of PREMIS in conjunction with METS
> > (only).
> I'm a little lost as to why this is a METS only issue. The redundancy
> issue does not crop up in any other context?
> If only a few elements are mandatory, then maybe its moot.
> > It should be clear that mandatory/optional contraints on PREMIS
> > elements/attributes should be dictated by the abstract PREMIS data
> > dictionary only.
> That does make sense to me, but it was suggested at the top of this
> thread that the definition of "mandatory" in the context of the data
> dictionary is not the same as the definition of "mandatory" in XML
That is true that the definition of mandatory in terms of the PREMIS data
dictionary is different from mandatory in terms of an XML schema (from
chapter 2 introduction to the data dictionary):
"Obligation: Whether a value for the semantic unit is mandatory (if
applicable) or optional
A mandatory semantic unit is something that the preservation repository
needs to know, independent of how or whether the repository records
it. The repository might not explicitly record a value for the semantic
unit if it is known by some other means (e.g., by the repository's
business rules). "Mandatory" actually means "mandatory if
applicable." For example, an identifier for a bitstream is mandatory only
if the repository manages data at the bitstream level. When exchanging
PREMIS-conformant metadata with another repository, values for mandatory
semantic units must always be provided.
Values for optional semantic units are encouraged but not required.
If a container unit is optional, but a semantic component within that
container is mandatory, the semantic component must be supplied if and
only if the container unit exists. That is, if a value for any of the
optional or mandatory semantic units in the container is supplied, a value
for all of the mandatory semantic units in the container must be
The working group spent a lot of time on mandatory vs. optional and came
up with this definition because of the variety of practices in and
implementations of preservation repositories. For instance, a repository
may use an object identifier that is unique in its own system, so although
objectIdentifierType is a mandatory element, it does not have to be
explicitly recorded within the repository. However, if the metadata and/or
object were exchanged, the type would need to be generated on
> > After all, isn't this why people define an abstract
> > model? See also the email sent by Ryan Chute on July 11 on this very list.
> Is there an archive of this list? I was not on it in July 11.
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