Re: [Scrollkeeper-devel] URN as identifier

[Dan M. <da...@ea...>]

On Mon, 23 Apr 2001, Bob Stayton wrote:

> > From: Dan Mueth <da...@ea...>
> > 
> > > But I'm not clear where a series ID fits into the OMF
> > > metadata DTD.  If I understand you correctly, the same
> > > series ID would be applied to every version/language/format
> > > of a document in its history, including when it changes
> > > hands.  But the OMF <identifier> element is supposed to be
> > > unique to each document.
> > 
> > Right.  So I guess the URN would go in identifier.  This can be done
> > without any modification to the OMF I believe.  (Is a URN considered a
> > URL?  If not, I guess we should explicitly state that an identifier may be
> > a URN.)
> 
> Well, if you look at the OMF template at
> http://www.ibiblio.org/osrt/omf/cgi-bin/template.pl
> the <identifier> element says "(e.g. a URL or URN)".
> The DTD uses "url" as the attribute name, but I believe
> that should be interpeted as a more general URI.

We should use the specification as the authoritative definition of the
OMF, as the DTD still needs some work until it is fully consistent with
the spec.  The spec is at: 
http://www.ibiblio.org/osrt/omf/omf_elements

As you say, it specifies "URL".  We can request this be changed to "URI"
for the next version of the specification.

> > eg:
> > <identifier>http://www.ldp.org/docs/howto/nfs</identifier>
> > <identifier>urn:blahblahblah</identifier>
> > 
> > If anybody replies to this, let's please start a new thread with a title
> > about URN's ;)
> > 
> > > I would propose instead using the OMF <relation> element,
> > > with its url attribute pointing to a series ID.  By that I
> > > mean define a seriesID using uuidgen as Dan suggests.  Then
> > > the OMF metadata for each document includes
> > > 
> > > <relation url="thisseriesUUID" status="omf-series-id"/>
> > > 
> > > This defines a relationship between this document and the
> > > series of which it is a part.  Then you could query an OMF
> > > metadata collection to select all documents that share the
> > > same relation element.  From that you could select specific
> > > alternate version/language/format documents.
> > > 
> > > Would this be a correct usage of the <relation> element?
> > > Would it meet the needs of a seriesID?
> > 
> > I think using a uuidgen code and putting it in RELATION is the way to
> > go.  (I was completely overlooking this element.)  I would propose
> > breaking RELATION into two attributes:  RELATION.identifier and
> > RELATION.seriesid.  The identifier attribute should follow the guidelines
> > of the IDENTIFIER element - it can point to any valid URL/URN.  The
> > seriesid is the document series id code, obtained from uuidgen.
> > 
> > It would look something like this:
> > 
> > -----
> > 14.     Relation
> >         Label: RELATION
> >         Obligation: Optional
> >                 RELATION.IDENTIFIER (Optional)
> >                 RELATION.SERIESID (Optional)
> >         Maximum Occurrence: Repeatable
> > 
> > Description of the resource's relationship with other similar resources.  
> > RELATION.IDENTIFIER is a URL that points to the IDENTIFIER element of
> > another resource.  Each instance of RELATION with the RELATION.IDENTIFIER
> > attribute links the resource to other resources of similar domain or
> > style. RELATION.SERIESID is a string code which specifies various
> > instances of a document, such as various versions, formats, or
> > translations.  All documents which are related in these ways should have
> > the same RELATION.SERIESID.  No documents which do not belong to this
> > set should share the RELATION.SERIESID.
> > -----
> 
> This sounds fine, but I'm trying to understand the
> OMF syntax for these.  As I read the existing
> OMF specification for VERSION, it has modifiers
> VERSION.identifier, VERSION.date, and VERSION.description.
> The description calls these attributes.  But the OMF
> DTD defines them as child elements of <version>.  I guess the
> spec uses the word "attribute" in the general meaning,
> not in the XML DTD meaning.  

Yes.  The specification doesn't distinguish between attributes and
children.  In most, if not all, cases we can treat these as children
instead of XML attributes. It looks like the current version of the DTD
treats some as children and others as attributes in self-closing
tags.

> If seriesid and identifier are children elements
> of <relation>, I'm not clear on how the <relation>
> XML attributes are used.  Perhaps we should contact
> someone at OMF to get clarification on the
> expected usage of <relation>?

I don't think it matters if what the specification calls "attributes" are
children or attributes in self-closing tags in the XML representation.

We could have:
<relation>
  <identifier>
     http:foo
  </identifier>
</relation>
<relation>
  <seriesid>
     1234567890
  </seriesid>
</relation>

Or:
<relation identifier="http:foo"/>
<relation seriesid="1234567890"/>

One thing which is not clear for this element or some of the other ones
is:

(1) Can you have both the identifier and the seriesid attributes set for a
given <relation>? I would expect this to be "no", since the identifier is
not describing the same object as the seriesid.

(2) Can you have multiple children of the same type (eg. two
<identifier>'s) for a given <relation>?  I would expect this to also be
"no", although the specification doesn't explicitly state it.

I would expect that the specification should explicitly address these
issues.

Dan